Green Synthesis and Characterizations of Cobalt Oxide Nanoparticles and Their Coherent Photocatalytic and Antibacterial Investigations

: Water pollution is a serious concern for developing and undeveloped countries. Photo-catalytic degradation of organic pollutants is an effective degradation method to restrain the green ecosystem. This research article presents a green, low-cost, and benevolent eco-friendly biosynthesis of cobalt oxide (Co 3 O 4 ) nanoparticles using Curcuma longa plant extract. The UV and visible region absorbance of Co 3 O 4 nanoparticles estimated the Co 2+ and Co 3+ transitions on the lattice oxygen, and their bandgap of 2.2 eV was conﬁrmed from the UV-DRS spectroscopy. The cubic structure and spherical shape of Co 3 O 4 nanoparticles were estimated by using XRD and TEM characterizations. Plant molecules aggregation and their agglomerations on the nanoparticles were established from FTIR and EDX spectroscopy. Multiple cobalt valences on the oxygen surfaces and their reaction, bonding, and binding energies were analyzed from XPS measurements. The biogenic Co 3 O 4 nanoparticles were executed against gram-positive ( Staphylococcus aureus — S. aureus ) and gram-negative ( Escherichia coli — E. coli ) bacteria. A gram-positive bacterial strain exhibited great resistivity on Co 3 O 4 nanoparticles. Degradation of organic dye pollutants on the Co 3 O 4 nanoparticles was performed against methylene blue (MB) dye under the conditions of visible light irradiation. Dye degradation efﬁciency pseudo-ﬁrst-order kinetics on the pseudo-ﬁrst-order kinetics denotes the rate of degradation over the MB dye. This research work achieved enhanced degradation potency against toxic organic dye and their radicals are excited from visible light irradiations. Absorption light and charged particle recom-binations are reformed and provoked by the plant extract bio-molecules. In this process, there is no inferior yield development, and electrons are robustly stimulated. Furthermore, the biosynthesized Co 3 O 4 nanoparticles determined the potency of bacterial susceptibility and catalytic efﬁcacy over the industrial dye pollutants.


Introduction
Water contamination is currently a serious environmental problem and a major menace to community physical conditions all over the human race as a consequence of the speedy Water 2023, 15, 910.https://doi.org/10.3390/w15050910https://www.mdpi.com/journal/wateradvancement of economies, manufacturers, and population growth [1,2].Most pollutant types include pesticides, dyes, pigments, phenol, organic contaminants, fungicides, e-waste, oil refineries, and so on [2,3].When compared to other types of water pollutants, organic dyes are one of the most significant sources of environmental pollution [4,5].Dye-based products attract a large portion of fast-moving consumer goods to humans because they are extensively used as color tones in the textile, printing, rubber, cosmetics, plastics, and leather industries [2][3][4][5][6].The presence of hazardous materials in industrial wastewater endangers human health and aquatic organisms in the environment.Dyes are categorized into three major types: anionic, cationic, and non-ionic.These dyes are very stable and can only be decomposed at temperatures above 200 • C [3][4][5][6].The presence of hazardous dye materials in industrial wastewater endangers human health and aquatic organisms in the environment [4][5][6].Among them, cationic dyes are more colorful but have some toxic properties for humans, the environment, and ecology [5,6].Methylene blue is a common cationic dye that is commonly applied in textiles, cosmetics, leather industries, paper industries, and foodstuffs [5,6].After implanting, these dyes into their applied goods inappropriate releases of this dye contaminant into the water bodies create a major problem.
It has been linked to several health risks, such as eye irritation, respiratory problems, gastrointestinal tract problems, and cerebral failure [6].
The elimination of the MB dye molecule from industrial effluent has been studied using a variety of methods, including enzymatic processes, photodegradation, chemical coagulation, electrochemical removal, ozonation, ion exchange, sonication, membrane filtration, and physical adsorption [7][8][9].Among these commercial methods, photocatalysis is gaining popularity due to its simple process, easy catalytic recovery, and low secondary pollution formation seismology [8,9].Zeolites, metal MXenes, metal oxides, conducting polymers, and other materials are used in dye treatments.Due to their remarkably high surface area and superior semiconducting properties, many transition metals and their oxide nanoparticles have been synthesized and tested for photocatalytic performance.Metal oxides such as ZnO, CuO, TiO 2 , AgO, and Co 3 O 4 are commonly used in photocatalytic dye degradation [8][9][10][11][12].
Among these, Co 3 O 4 in particular demonstrated an impressively extensive application for catalysts, sensors, magnetic materials, and energy storage electrode materials [12].The methods used to prepare these metal oxides, such as sol-gel, hydrothermal, electrochemical, solvent evaporation, co-precipitation, and green synthesis, are extensively used.Among them, green synthesis is a low-cost, environmentally friendly, and simple method for producing metal oxide nanoparticles [13].Many green-mediated metal oxide syntheses are ZnO, Fe 2 O 3 , AgO, CuO, and Al 2 O 3 using plant sources such as Agathosma betulina, Sida cordifolia, Pedalium murex, Gloriosa superba, and Prunus yedoensis [14].Curcuma longa is a tropical rhizomatous mostly extensively cultivated in India.The medicinal benefits of Curcuma longa include anti-inflammatory, antimicrobial, antiseptic, anti-fungal, antiallergenic, antioxidant, anthelmintic, antimalarial, antiallergic activity, antiarthritic, antiulcer, antidiabetic, antiaging, anti-mutagenic and anti-cancer activity [15][16][17][18][19].For the green synthesis of metal oxide using curcumin as a reducing agent for different nanoparticle preparations by assembling the work presented in many works of literature.In general, green synthesis involves two vital steps in the synthesis of nanoparticles.Curcumin, as a reducing agent, provides metal reduction from M x+ to M 0 while also stabilizing the formation of arbitrary aggregation and controlling the size and shape of the nanoparticles [20][21][22].
The present work focuses on three major points, which are: (i) The metal oxide Co 3 O 4 nanoparticles are constructed using green synthesis curcumin extract.The plant extract helps to attain the nanostructure formation, reduced the light recombined activity and increased the ROS activities.(ii) Organic contaminants of MB dye were removed from aquatic surfaces through the photocatalysis method under visible light irradiation.Bacterial strains of E. coli and S. aurues are eradicated by using Co 3 O 4 nanoparticles.

Materials
Cobalt nitrate hexahydrate (Co(NO 3 ) 2 .6H 2 O) and Methylene Blue (C 16 H 18 CIN 3 S) was acquired from HiMedia, Mumbai, India.The purchased chemicals were obtained at 99.9% purity in analytical reagent (AR) grade, and no extra refinement occurred in the synthesis time.The fresh leaf of the Curcuma longa plant was collected from Kerala, India.

Plant Extract Preparation
The Curcuma longa plant leaves (5 g of fresh leaves) were washed with running tap water.The round bottom flask was used to combine the cleaned green leaf and 100 mL double distilled water.The combinations of leaf and distilled water were heated for 30 min at 60 • C, and Whatman No. 1 filter paper was used to filter the sediment.The obtained pure leaf extract solution was kept at 4 • C conditions for further evolutions.

Biosynthesis of Co 3 O 4 Nanoparticles
0.1 M Cobalt nitrate hexahydrate (Co(NO 3 ) 2 .6H 2 O) and 10 mL plant extract of Curcuma longa were used in the nanoparticle synthesis process.Both sources were mixed by using a magnetic stirrer at constant rpm (750 rpm) for 30 min.The color deviations from light brown to dark brown specify the nucleation and growth of Co 3 O 4 nanoparticles.The obtained color-modified nanoparticle solutions were centrifuged at 10,000 rpm for 10 min (repeated three times), and their obtained pellet was washed with double distilled water.Finally, the collected nanoparticle precipitate was filtered (with Whatman No. 1 filter paper) and dried in the oven at 100 • C for 60 min.The dried nanoparticle samples were processed for further measurements [23,24].

Characterization of Nanoparticles
Structural phase and material crystallinity are evaluated from XRD (PANalytical X'Pert Pro Diffractometer; radiation = Cu Kα (1.5405 Å); working condition = 30 kV and 40 mA) analysis.The nanoparticle formation, reaction, and functional group involvement were captured by Perkin Elmer FT-IR spectroscopy, and their wavelength limit is 4000 cm −1 to 400 cm −1 .The optical imperfections and their transition properties were observed from UVvisible DRS (UV-2600 Shimadzu) analysis.The nano-sized surface structural modification and their elemental compositions were analyzed from FESEM (Carl Zeiss) and TEM (Titan) with EDX spectroscopy.The valency, bonding, and binding energies of the synthesized nanoparticles were characterized by using x-ray photoelectron spectroscopy (XPS; PHI 5000 Versa Probe III, Physical Electronics, Chanhassen, USA) [23,24].

Photocatalytic Activity
The photocatalytic activity of biosynthesized Co 3 O 4 nanoparticles was examined using the organic effluent of MB dye.The visible light source (Xenon lamp wavelength = 400 nm) irradiated the Co 3 O 4 nanoparticles.The 10 mg of Co 3 O 4 nanoparticles were mixed with 100 mL (10-ppm) of MB dye solution by using a magnetic stirrer and kept in a dark environment for 40 min.The dark condition stirring process helps to attain the adsorption-desorption equilibrium positions.Visible light photocatalytic activity of Co 3 O 4 nanoparticles and dye solution were processed by closed chamber xenon lamp irradiation.The light irradiation dissociated the dye bonding and decreased the absorbance strength over the catalyst; it was measured at 10 min intervals.10 min time gap, the dye solution was taken out and centrifuged for 1000 rpm to remove the catalyst from the dye solution and measured in UV-Visible spectroscopy.The dissociated dye absorbance was calculated [25][26][27].

Antibacterial Activity
The microbial resistance of Co 3 O 4 nanoparticles was measured in gram-positive Staphylococcus aureus (ATCC 6538) and gram-negative Escherichia coli (ATCC 8739) through the well diffusion method.The 10 6 CFU/mL concentrated bacterial culture was inoculated into the nutrient broth and placed in the incubator for overnight incubation.The Muller-Hinton agar medium was poured into sterilized Petri plates and incubated overnight, and the growing culture was swabbed on the sterilized Petri plates.The 5 mm holes were made by the gel puncture method in the Muller-Hinton agar plates, and the holes were filled with different concentrations of Co 3 O 4 nanoparticles (10, 20, 50, and 100 µg/mL) nanoparticles.Then, the plates were incubated at 37 • C for 24 h.The cell death and deactivation were assessed by the development of a clear zone around the holes, which was measured on a millimeter (mm) scale [27].

XRD Analysis
The biosynthesized Co 3 O 4 nanoparticles' x-ray diffractive pattern is presented in Figure 1.The diffraction peaks of Co 3 O 4 nanoparticles appearing at 2θ = 19.00220), (311), ( 222), (400), and (511) planes.The obtained Co 3 O 4 nanoparticles peaks are well-coincided with the cubic structure of standard JCPDS card number 042-1467 [28].The bio-molecule interaction on the cobalt sources exhibited the cobalt and oxygen nucleation sites and attracted each other by electron donor of plant molecules, which derived the Co 3 O 4 nanoparticles.The high-intensity peak of 36.88 • represents the high crystallinity and lattice strain of Co 3 O 4 nanoparticles.The crystallite size of Co 3 O 4 nanoparticles was determined by using the Debye-Scherrer formula [29].The obtained 26 nm, the crystallite size of cubic Co 3 O 4 nanoparticles, derived the narrow crystallite size, and it emanated the high electron accumulation of the surfaces.The smallest crystallite size increased the surface area, which enhanced the degradation capability of the hazardous dyes and organic substances.

FTIR Analysis
The Co 3 O 4 nanoparticle purity, plant extract bio-molecule qualitative measurement, and surface modifications were determined by FTIR spectroscopy and displayed in Figure 2. The cobalt oxide nanoparticles FTIR spectrum derived the cobalt, oxygen and reaction involved plant nutrients.FT-IR results for plant extract revealed absorption bands at 3261 cm −1 and 1636 cm −1 .The broad peak at 3261 cm −1 indicates O-H stretching vibrations and absorbed water molecules in the plant extract.The sharp peak at 1636 cm −1 indicates the presence of amides.The phytochemicals, such as terpenoids, alkaloids, phenols, steroids, and flavonoids, are mostly found in the C. longa extract.After the addition of C. longa leaf extract to the cobalt nitrate solution, the color change indicates the formation of Co 3 O 4 nanoparticles.Curcumin, one of the major polyphenolic compounds found in the C. longa plant, might be involved in the synthesis of copper oxide and nickel oxide nanoparticles.Herein, the Co 2+ ions were reduced to form Co 3 O 4 nanoparticles by donating the electrons from curcumin.The broad two prominent peaks are indicating the formation of Co 3 O 4 nanoparticles at 555 cm −1 and 659 cm −1 [30,31].Co(III)-O bonds were obtained from 659 cm −1 Co-O stretching vibrations associated with 555 cm −1 .The plant extract produced amide and carboxylic acid on the cobalt materials, which can be used for the reduction, capping, and stabilization of Co 3 O 4 nanoparticles [32,33].The minor peaks of 1382 cm −1 and 1639 cm −1 denote the amide and carboxylic acid from plant biomolecules.The water molecule and carbon attachment on the surfaces were observed from the peaks of 2331 cm −1 and 3415 cm −1 it representing the -OH stretching and C=O asymmetric vibration of the CO 2 molecule [34][35][36].The existing carbon and OH molecules are responsible for the reduction and enhanced activity of Co 3 O 4 nanoparticles.

FTIR Analysis
The Co3O4 nanoparticle purity, plant extract bio-molecule qualitative measurement, and surface modifications were determined by FTIR spectroscopy and displayed in Figure

UV-DRS Analysis
The absorbance and bandgap spectra of green-mediated Co3O4 nanoparticles are displayed in Figure 3.The green-mediated Co3O4 nanoparticles establishment was identified from the absorbance peaks at 380 and 690 nm [37,38].Broad two-peaks from green-mediated Co3O4 nanoparticles elucidated the transition of charges from O to Co orbitals.Co 2+ and Co 3+ orbital electrons move towards the O 2-, which indicates the double oxidation state of cobalt elements [37,38].P-type green-mediated Co3O4 nanoparticles optical imperfections were derived from Kubelka-Munk relations.Green-mediated Co3O4 nanoparticles calculated bandgap is 3.4 eV, which was well matched with previously reported

UV-DRS Analysis
The absorbance and bandgap spectra of green-mediated Co 3 O 4 nanoparticles are displayed in Figure 3.The green-mediated Co 3 O 4 nanoparticles establishment was identified from the absorbance peaks at 380 and 690 nm [37,38].Broad two-peaks from green-mediated Co 3 O 4 nanoparticles elucidated the transition of charges from O to Co orbitals.Co 2+ and Co 3+ orbital electrons move towards the O 2-, which indicates the double oxidation state of cobalt elements [37,38].P-type green-mediated Co 3 O 4 nanoparticles optical imperfections were derived from Kubelka-Munk relations.Green-mediated Co 3 O 4 nanoparticles calculated bandgap is 3.4 eV, which was well matched with previously reported Co 3 O 4 nanoparticles [39].The wide bandgap of Co 3 O 4 nanoparticles explained the gap between the holes and electrons, which suppressed the recombined activity.The obtained photo exciton charge carriers provoke the oxygen vacancy on the Co 3 O 4 nanoparticles [39].The charge carrier mitigations and partings may deduce the organic pollutants and deactivate the bacterial system in wastewater and biomedical applications.

FESEM with EDX Analysis
Surface morphological and elemental analysis of biogenic synthesized Co3O4 nanoparticles studied by FESEM with EDX and their belongings are displayed in Figure 4a-d.Spherical-shaped and mixed spherical nanoparticle morphologies were observed in biogenically synthesized Co3O4 nanoparticles.The spherical shape of Co3O4 nanoparticles was achieved through the nucleation, growth, and aggragation of the synthesized materials.Mixed shaped Co3O4 nanoparticles were obtained from the aggomeleration of synthesized Co3O4 nanoparticles due to the capped plant molecules.Plant derivatives controlled the nucleation, growth, and structuring of nanoparticles, and their enriched quantities of phytonutrients agglomerated the biogenically synthesized Co3O4 nanoparticles [40,41].Metal and oxygen stabilization/interface formed the nanostructure of biogenically synthesized Co3O4 nanoparticles.EDX spectroscopy of biogenically synthesized Co3O4 nanoparticles confirmed the existing elements of Co and O (Figure 4c,d).Their Co and O presence elucidates the phase of pure biogenically synthesized Co3O4 nanoparticles, and no other element is evolved in the reactions.Metal compound occurrence is high in the biogenically synthesized Co3O4 nanoparticles because of their lattice oxygen stabilization [41][42][43].Further, the oxygen vacancy was stabilized and filled by cobalt cations, and their values are presented in Figure 4d.

FESEM with EDX Analysis
Surface morphological and elemental analysis of biogenic synthesized Co 3 O 4 nanoparticles studied by FESEM with EDX and their belongings are displayed in Figure 4a-d

TEM Analysis
The TEM analysis examined the surface morphology and particle size of the biogenically synthesized Co3O4 nanoparticles.The two different magnifications with two different parts of biogenically synthesized Co3O4 nanoparticles are exhibited in Figure 5a,b.The biogenically synthesized Co3O4 nanoparticles revealed the spherical shape and lite black surroundings over spherical and conjoint spherical shapes representing the plant molecules encapsulations [44,45].The plant molecule encapsulations over the biogenically synthesized Co3O4 nanoparticles are relieved from FTIR and XPS analysis.The particle size of biogenically synthesized Co3O4 nanoparticles is 22 nm.The obtained particle size values denoted the lattice constraint between the cobalt and oxygen, and their electron mobilization was evident from XRD and UV-DRS analysis.

TEM Analysis
The TEM analysis examined the surface morphology and particle size of the biogenically synthesized Co

XPS Analysis
The XPS analysis examined the chemical valency and binding energy of the biogenically synthesized Co3O4 nanoparticles.The valency of the material is determined by the catalytic efficiency of the synthesized compounds.The XPS spectrum displays the wide, Co, O, and C elements from biogenically synthesized Co3O4 nanoparticles, as displayed in Figures 6a-d.A wide spectrum of biogenically synthesized Co3O4 nanoparticles presented Co, O, and C elements (Figure 6a).The Co and O elements confirmed the formation of Co3O4 nanoparticles, and the C elements come from plant extract.The Co elements are represented by two major peaks and their Co-2p state existence in 796 eV= Co-2p1/2 and 780.2 eV = Co-2p3/2 respectively (Figure 6b).The Co double splitting is well documented with the previously reported work and standard Co element [46,47].The O spectrum is located at 529-531 eV, and its valency is O-1s (Figure 6c).The lattice oxygen peaks complete the reaction of the biogenically synthesized Co3O4 nanoparticles, and their interface was led by the plant nutrients [46].The cationic metals interacted with the organic plant molecules, and they could create oxygen vacancies on the surfaces.Three peaks were obtained in the O-1s XPS spectrum, including lattice oxygen, surface oxygen, and oxygen defect.The oxygen spectra determined the robust interface between metal and plant organic molecules.The absorbed oxygen on cationic metal is established the metal oxide nanostructure [47].The plant extract reduced the zero valent cobalt and re-oriented it with lattice oxygen, which formed the biogenically synthesized Co3O4 nanoparticles.The bioreduction of the biogenically synthesized Co3O4 nanoparticles was assured by the C-1s peak (Figure 6d).The three different small peaks are depicted in the C-O, C-C, and C=O bonds, which provoke the reduction and stabilization of Co and O elements to produce the biogenically synthesized Co3O4 nanoparticles [47,48].Further, the attained findings confirmed the high-purity biogenic synthesized Co3O4 nanoparticles.

XPS Analysis
The XPS analysis examined the chemical valency and binding energy of the biogenically synthesized Co  6b).The Co double splitting is well documented with the previously reported work and standard Co element [46,47].The O spectrum is located at 529-531 eV, and its valency is O-1s (Figure 6c).The lattice oxygen peaks complete the reaction of the biogenically synthesized Co 3 O 4 nanoparticles, and their interface was led by the plant nutrients [46].The cationic metals interacted with the organic plant molecules, and they could create oxygen vacancies on the surfaces.Three peaks were obtained in the O-1s XPS spectrum, including lattice oxygen, surface oxygen, and oxygen defect.The oxygen spectra determined the robust interface between metal and plant organic molecules.The absorbed oxygen on cationic metal is established the metal oxide nanostructure [47].The plant extract reduced the zero valent cobalt and re-oriented it with lattice oxygen, which formed the biogenically synthesized Co

Photocatalytic Dye Degradation
Photocatalytic degradation of MB was studied using as-synthesized Co3O4 nanoparticles under visible light irradiation.The visual color of the treated dye and UV-vis spectrum are shown in Figure 7a.In this present case, the photocatalyst, Co3O4 nanoparticles, has a complex spinel structure in which Co 2+ ions occupy tetrahedral sites and Co 3+ ions occupy octahedral sites of the cubic close-packed lattice of oxide anions [49].The valance band is characterized by the (2p) orbital having O2 -carriers, whereas the 3d orbital contributes Co 2+ carriers in the conduction band.As a result, the charge transfer band (O2 -to Co 2+ ) that appears in the wavelength range 400-800 nm is the primary governing factor for Co3O4 nanoparticle-based photocatalytic processes.When photons were illuminated, the methylene blue dye produced reactive species that inserted electrons back into the lattice plane of Co3O4 nanoparticles, assisting in the creation of superoxide radicals in the presence of accessible oxygen in the solution, further enhancing the photodegradation process.The breakdown of the chromophoric group and the transformation of dye into low molecular weight by-products are connected with the photocatalytic degradation of the target dye [50].Under visible light irradiation, dye degradation is primarily caused by the creation of electrons (e -) and holes (h + ) on the catalyst surface.Water molecules mix with holes h + to form the OH radical.The O2 molecule scavenges the electrons e -and converts them to OH through HOO and H2O2 intermediates.The OH is a powerful oxidizing species that non-selectively degrades the organic molecule dye into H2O, CO2, and inorganic ions [51].The same work was repeated three times with the same experimental conditions, and their standard deviation values were calculated.The MB dye degradation (90%) during the 40-min radiation exposure is depicted in figure (b).The rates of

Photocatalytic Dye Degradation
Photocatalytic degradation of MB was studied using as-synthesized Co 3 O 4 nanoparticles under visible light irradiation.The visual color of the treated dye and UV-vis spectrum are shown in Figure 7a.In this present case, the photocatalyst, Co 3 O 4 nanoparticles, has a complex spinel structure in which Co 2+ ions occupy tetrahedral sites and Co 3+ ions occupy octahedral sites of the cubic close-packed lattice of oxide anions [49].The valance band is characterized by the (2p) orbital having O 2 − carriers, whereas the 3d orbital contributes Co 2+ carriers in the conduction band.As a result, the charge transfer band (O 2 − to Co 2+ ) that appears in the wavelength range 400-800 nm is the primary governing factor for Co 3 O 4 nanoparticle-based photocatalytic processes.When photons were illuminated, the methylene blue dye produced reactive species that inserted electrons back into the lattice plane of Co 3 O 4 nanoparticles, assisting in the creation of superoxide radicals in the presence of accessible oxygen in the solution, further enhancing the photodegradation process.The breakdown of the chromophoric group and the transformation of dye into low molecular weight by-products are connected with the photocatalytic degradation of the target dye [50].Under visible light irradiation, dye degradation is primarily caused by the creation of electrons (e − ) and holes (h + ) on the catalyst surface.Water molecules mix with holes h + to form the OH radical.The O 2 molecule scavenges the electrons e − and converts them to OH through HOO and H 2 O 2 intermediates.The OH is a powerful oxidizing species that non-selectively degrades the organic molecule dye into H 2 O, CO 2 , and inorganic ions [51].The same work was repeated three times with the same experimental conditions, and their standard deviation values were calculated.The MB dye degradation (90%) during the 40-min radiation exposure is depicted in figure (b).The rates of methylene blue degradation using Co 3 O 4 photocatalyst were determined from the graph of ln(Co/Ct) vs time (min).The kinetic study infers the pace of the order of the reaction.The graph depicts a straight line with a positive slope and a rate constant of 0.05468 min −1 for Co 3 O 4 nanoparticles.The mechanism of photodegradation is shown in Equations ( 1)-( 7).

Effect of Catalyst Dosage
The various catalyst dosages were scrutinized against the MB dye solution.The photocatalytic dye degradation of various catalyst concentrations was demonstrated in Figure 8.A low catalyst dosage of 1 mg causes 58% degradation and 5 mg causes 69% degradation against MB dye.The excitation of electrons and light absorption is based on the catalyst surface area, and it can be motivated by radical genericity.10 mg catalyst dosage is optimized concentrations of Co3O4 nanoparticles than 1 mg, 5 mg and 15 mg (71%) Co3O4 nanoparticles.The high surface area and OH radical productivities destroyed the dye bonding and increased the active sites of the nanomaterial surfaces.The 15 mg of Co3O4 nanoparticles restricted the electron mitigations from different bands due to their high occupations, which do not allow light movements that can suppress the charge carrier multiplicity.Therefore, 10 mg of Co3O4 nanoparticles are produced for improved photocatalytic dye degradation.

Photodegradation Mechanism
The degradation of organic pollutants is influenced by various parameters such as light source, surface area, bandgap, sizes, ion releasing capacity, dye concentration and catalyst dosage etc.The cobalt oxide nanoparticle degradation of various dye solutions is listed in Table 1.The present work degradation efficiency is compared with previous reported work, and the obtained degradation is expressed as the enhanced degradation potential of published work [52][53][54][55][56][57][58][59][60][61].

Effect of Catalyst Dosage
The various catalyst dosages were scrutinized against the MB dye solution.The photocatalytic dye degradation of various catalyst concentrations was demonstrated in Figure 8.A low catalyst dosage of 1 mg causes 58% degradation and 5 mg causes 69% degradation against MB dye.The excitation of electrons and light absorption is based on the catalyst surface area, and it can be motivated by radical genericity.10 mg catalyst dosage is optimized concentrations of Co 3 O 4 nanoparticles than 1 mg, 5 mg and 15 mg (71%) Co 3 O 4 nanoparticles.The high surface area and OH radical productivities destroyed the dye bonding and increased the active sites of the nanomaterial surfaces.The 15 mg of Co 3 O 4 nanoparticles restricted the electron mitigations from different bands due to their high occupations, which do not allow light movements that can suppress the charge carrier multiplicity.Therefore, 10 mg of Co 3 O 4 nanoparticles are produced for improved photocatalytic dye degradation.

Antibacterial Activity
Bacterial contamination leads to a variety of issues for all, such as infection, mortality, and organ defects, which are controlled by antibiotics.The high usage of antibiotics is expressed by the many irregularities and the complete suppression of the bacterial domains.Good bacteria are also degraded by antibiotics, and their long-term use inhibits the nerve action system.Hence, researchers are focusing to raise innovative techniques to reduce the hazardous evolution and dispersion.Nanophase materials are always a new and effective antibacterial output for the scientific community.Biogenic nanoparticles give a superior bacterial resistive property in various bacterial strains [62].The present study of biogenic Co 3 O 4 nanoparticles showed significant bacterial output against E. coli and S. aureus bacterial strains.The results of using Co 3 O 4 nanoparticles showed an increased zone of inhibition with increasing nanoparticle concentrations [63][64][65].The inhibited bacterial plate was shown in Figure 9.The statistical analysis of the Co 3 O 4 nanoparticles antibacterial activity was calculated.The zone of inhibitions tells the sensitivity and resistivity of Co 3 O 4 nanoparticles.Gram-positive bacteria of S. aureus have a higher effective sensitivity than gram-negative bacteria of E. coli.The lipopolysaccharide protected cell wall could not be easily destructed by the metal ions due to its thickness.Peptidoglycan-covered cell wall bacterial strains are easily penetrated by nanoparticles due to their 80 nm layered thickness of the cell wall [62][63][64][65][66].This is the main reason for the metal ions entry into the interactions of the bacterial structure.The disrupted cell wall permits the Co 3 O 4 nanoparticles, and it provokes ROS production.Increased toxic levels in the cell system suppressed the nucleus and DNA production.Without nutrients, a cell body lost its energy, which stopped the cell active signaling and induced the cell demise.

Antibacterial Activity
Bacterial contamination leads to a variety of issues for all, such as infection, mortality, and organ defects, which are controlled by antibiotics.The high usage of antibiotics is expressed by the many irregularities and the complete suppression of the bacterial domains.Good bacteria are also degraded by antibiotics, and their long-term use inhibits the nerve action system.Hence, researchers are focusing to raise innovative techniques to reduce the hazardous evolution and dispersion.Nanophase materials are always a new and effective antibacterial output for the scientific community.Biogenic nanoparticles give a superior bacterial resistive property in various bacterial strains [62].The present study of biogenic Co3O4 nanoparticles showed significant bacterial output against E. coli and S. aureus bacterial strains.The results of using Co3O4 nanoparticles showed an increased zone of inhibition with increasing nanoparticle concentrations [63][64][65].The inhibited bacterial plate was shown in Figure 9.The statistical analysis of the Co3O4 nanoparticles antibacterial activity was calculated.The zone of inhibitions tells the sensitivity and resistivity of Co3O4 nanoparticles.Gram-positive bacteria of S. aureus have a higher effective sensitivity than gram-negative bacteria of E. coli.The lipopolysaccharide protected cell wall could not be easily destructed by the metal ions due to its thickness.Peptidoglycan-covered cell wall bacterial strains are easily penetrated by nanoparticles due to their 80 nm layered thickness of the cell wall [62][63][64][65][66].This is the main reason for the metal ions entry into the interactions of the bacterial structure.The disrupted cell wall permits the Co3O4 nanoparticles, and it provokes ROS production.Increased toxic levels in the cell system suppressed the nucleus and DNA production.Without nutrients, a cell body lost its energy, which stopped the cell active signaling and induced the cell demise.

Conclusions
Bio-mediated nanophase material constructions are gaining extra attention in all research sectors due to their noxious, cost-effective, and pollution-free method of synthesis.Curcuma longa plant extract achieved the in-situ reduction of valence-free cobalt atoms

Conclusions
Bio-mediated nanophase material constructions are gaining extra attention in all research sectors due to their noxious, cost-effective, and pollution-free method of synthesis.Curcuma longa plant extract achieved the in-situ reduction of valence-free cobalt atoms and encouraged lattice oxygen stabilizations.The crystallite size and spherical morphologies of the Curcuma longa-derived Co

2 .
The cobalt oxide nanoparticles FTIR spectrum derived the cobalt, oxygen and reaction involved plant nutrients.FT-IR results for plant extract revealed absorption bands at 3261 cm −1 and 1636 cm −1 .The broad peak at 3261 cm −1 indicates O-H stretching vibrations and absorbed water molecules in the plant extract.The sharp peak at 1636 cm −1 indicates the presence of amides.The phytochemicals, such as terpenoids, alkaloids, phenols, steroids, and flavonoids, are mostly found in the C. longa extract.After the addition of C. longa leaf extract to the cobalt nitrate solution, the color change indicates the formation of Co3O4 nanoparticles.Curcumin, one of the major polyphenolic compounds found in the C. longa plant, might be involved in the synthesis of copper oxide and nickel oxide nanoparticles.Herein, the Co 2+ ions were reduced to form Co3O4 nanoparticles by donating the electrons from curcumin.The broad two prominent peaks are indicating the formation of Co3O4 nanoparticles at 555 cm −1 and 659 cm −1 [30,31].Co(III)-O bonds were obtained from 659 cm −1 Co-O stretching vibrations associated with 555 cm −1 .The plant extract produced
. Spherical-shaped and mixed spherical nanoparticle morphologies were observed in biogenically synthesized Co 3 O 4 nanoparticles.The spherical shape of Co 3 O 4 nanoparticles was achieved through the nucleation, growth, and aggragation of the synthesized materials.Mixed shaped Co 3 O 4 nanoparticles were obtained from the aggomeleration of synthesized Co 3 O 4 nanoparticles due to the capped plant molecules.Plant derivatives controlled the nucleation, growth, and structuring of nanoparticles, and their enriched quantities of phytonutrients agglomerated the biogenically synthesized Co 3 O 4 nanoparticles [40,41].Metal and oxygen stabilization/interface formed the nanostructure of biogenically synthesized Co 3 O 4 nanoparticles.EDX spectroscopy of biogenically synthesized Co 3 O 4 nanoparticles confirmed the existing elements of Co and O (Figure 4c,d).Their Co and O presence elucidates the phase of pure biogenically synthesized Co 3 O 4 nanoparticles, and no other element is evolved in the reactions.Metal compound occurrence is high in the biogenically synthesized Co 3 O 4 nanoparticles because of their lattice oxygen stabilization [41-43].Further, the oxygen vacancy was stabilized and filled by cobalt cations, and their values are presented in Figure 4d.
3 O 4 nanoparticles.The two different magnifications with two different parts of biogenically synthesized Co 3 O 4 nanoparticles are exhibited in Figure 5a,b.The biogenically synthesized Co 3 O 4 nanoparticles revealed the spherical shape and lite black surroundings over spherical and conjoint spherical shapes representing the plant molecules encapsulations [44,45].The plant molecule encapsulations over the biogenically synthesized Co 3 O 4 nanoparticles are relieved from FTIR and XPS analysis.The particle size of biogenically synthesized Co 3 O 4 nanoparticles is 22 nm.The obtained particle size values denoted the lattice constraint between the cobalt and oxygen, and their electron mobilization was evident from XRD and UV-DRS analysis.
3 O 4 nanoparticles.The valency of the material is determined by the catalytic efficiency of the synthesized compounds.The XPS spectrum displays the wide, Co, O, and C elements from biogenically synthesized Co 3 O 4 nanoparticles, as displayed in Figure 6a-d.A wide spectrum of biogenically synthesized Co 3 O 4 nanoparticles presented Co, O, and C elements (Figure 6a).The Co and O elements confirmed the formation of Co 3 O 4 nanoparticles, and the C elements come from plant extract.The Co elements are represented by two major peaks and their Co-2p state existence in 796 eV = Co-2p 1/2 and 780.2 eV = Co-2p 3/2 respectively (Figure 3 O 4 nanoparticles.The bio-reduction of the biogenically synthesized Co 3 O 4 nanoparticles was assured by the C-1s peak (Figure 6d).The three different small peaks are depicted in the C-O, C-C, and C=O bonds, which provoke the reduction and stabilization of Co and O elements to produce the biogenically synthesized Co 3 O 4 nanoparticles [47,48].Further, the attained findings confirmed the high-purity biogenic synthesized Co 3 O 4 nanoparticles.

Figure 9 .
Figure 9. Antibacterial activity of Co 3 O 4 nanoparticles against S. aureus and E. coli with different concentrations.
3 O 4 nanoparticles designate their 26 nm size and a large area on the surfaces of the Co 3 O 4 nanoparticles.The optical and chemical valency of the Co 3 O 4 nanoparticles projected the Co 2+ and Co 3+ valency over the oxygen vacancies.Electronic transitions of Co 3 O 4 nanoparticles specify the formation of Co and O stabilization and improved the material interface by plant extract of Curcuma longa.Biogenic Co 3 O 4 nanoparticles exhibited enhanced antibacterial efficiency in gram-positive bacterial strains.Visible light photocatalytic dye degradation activity of Co 3 O 4 nanoparticles was investigated against MB dye under and obtained the degradation is 90%.The double valency of Co 3 O 4 nanoparticles increases the lifetime of electron-hole pair recombination and intensifies the oxidation and reduction properties against the MB dye.Therefore, oxidation of Co 3 O 4 nanoparticles enhanced the parting of charge particles, enlarged the radical speciation, and produced noxious-free end products.Consequently, obtained results advocate the Co 3 O 4 nanoparticles can be used for further growth and applications in the water-treatment process and biomedical-related areas.

Table 1 .
Comparison table of Co 3 O 4 nanoparticles degradation against different conditions.