Biosynthesis of JC-La2CoO4 magnetic nanoparticles explored in catalytic and SMMs properties

We have reported the synthesis of JC-La2CoO4 magnetic nanoparticles from Jatropha Curcas L. leaf extract in aqueous medium and potential application study in catalytic & Single Molecule Magnets (SMMs). Several techniques were used to investigate the structural, morphological, and elemental composition, particle size, optical properties, catalytic and magnetic properties by XRD, FTIR, SEM, EDAX, XPS, UV–visible and squid magnetic measurement. It was found that the crystallite sizes and grain sizes of JC-La2CoO4 NPs were 11.3 ± 1 and 24.1 ± 1 nm respectively and surface morphology of the nanoparticles looks spherical shape with good surface area. The band gap of JC-La2CoO4 was found to be 4.95 eV indicates good semiconductor in nature. XPS studies shows that La and Co present in + 3 and + 2 oxidation state respectively and suggest the composition formula is La2CoO4 with satisfied all the valency of metal ions. The photocatalytic efficiency of La2CoO4 shows good result against methylene blue (MB) compared to other dyes like MO, NO, RhB in presence of sunlight with rate constant 56.73 × 10–3 min-1 and completely degraded within 115 mints. The importance of JC-La2CoO4 has magnetic properties with antiferromagnetic coupling and SMMs properties with nature.


Plant materials
Jatropha curcas L. (family: Euphorbiaceae) is a perennial shrub widely cultivated in the Amarkantak region as a living fence (hedge) in the fields and human settlements.The IUCN status of the Plant is 'Least concern' .The authentication of the plant species was identified by a plant taxonomist (Dr.Ravindra Shukla) and its physical specimen (IGNTU/DoB/2023/Eup/JC/06) was lodged in the herbarium of the Department of Botany, Indira Gandhi National Tribal University, Amarkantak as per national, and international guidelines and legislation.The wild plant Jatropha curcas (JC) leaves were collected by Ghorai Research Group (N.Satpute, A. Kesharwani and M. K. Ghosh) from the Podki near the Indira Gandhi National Tribal University, Amarkantak, Madhya Pradesh, India in the month of April 2023 (Fig. 1).The research work of JC was completed in the Department of Chemistry, Nanomaterials & Crystal Design Laboratory, Indira Gandhi National Tribal University, Madhya Pradesh, Amarkantak, India.

Bio-synthesis of JC-La 2 CoO 4 NPs
At first, La(NO 3 ) 3 (0.389 g, 10 mM) was taken in a 200 ml beaker and dissolved in 90 mL of DDW.After that, 10 mL of JC leave extract was added to the La(NO 3 ) 3 solution with a 9:1 ratio, and the mixture was kept at room temperature and stirred for about 15 min.In another beaker, a Co(NO 3 ) 2 (0.262 g, 10 mM) solution was prepared by dissolving in 90 mL of DDW.After that, cobalt nitrate solution was added to the mixture of JC-La-extract and stirred constantly for about 2 h and then the mixture was kept in a hot air oven at 35 °C for overnight.A greenish yellow viscous solution of JC-La 2 CoO 4 NPs has been obtained as a suspended particle and confirmed by UV-visible spectroscopy measurement.The pH of the reaction mixture is 4.15 during the preparation of JC-La 2 CoO 4 NPs.Finally, the resultant solution was centrifuged at 11,000 rpm for 15 min at room temperature and JC-La 2 CoO 4 NPs were precipitated at the bottom of the centrifuge tube, filtered and washed with purified water, dried in an oven at 80 °C for 2 h and collected as brown JC-La 2 CoO 4 for further characterization.A phytochemical test of JC was performed and it may act as reducing as well as capping and stabilizing agents for the green synthesis of JC-Co 2 LaO 4 NPs.The schematic representation of JC-Co 2 LaO 4 is shown in the Fig. 1.

Characterization techniques
JC-La 2 CoO 4 NPs formation, optical property, and photocatalytic activity have been characterized by the use of the UV visible spectrophotometer (Shimadzu UV-1800).The crystal structure of JC-La 2 CoO 4 NPs was measured by Powder X-ray diffraction (XRD) at room temperature by using Xʹ Pert3 Panalytical, equipped with Cu Kα (1.54060 Å) as the incident radiation.Scherer equation was used for calculation of crystallite size.The Scherer equation was D = Kλ/βcosӨ, K = 0.9, D = Crystal size (Å), λ = Wavelength of Cu-Kα radiation, and β = Corrected half width of the diffraction peak.Nicolet iS5 (Thermo Scientific) was used for FT-IR analysis of samples at room temperature.The surface morphology and elemental composition of the fine NPs were analysed by Scanning Electronic Microscopy (SEM) and EDAX (SEM-EDAX: JEOL 6390LA/ OXFORD XMX N).Oxidation state of metals with presence of elemental % of nanomaterial measured by X-ray Photoelectron Spectroscopy (Thermo Fisher Scientific: Escalab Xi+).Magnetic Study of prepared sample DC and AC magnetic susceptibility were carried out on Superconducting Quantum Interference Device Magnetometry.Quantum Design MPMS-XL SQUID magnetometer (IISER Bhopal) equipped with a 7-T magnet and operating in the 1.8 to 300-K range was used on vacuum dried solids to collect variable-temperature dc and ac magnetic susceptibility data.

FTIR analysis
The vibrational property of the Jatropha Curcas leaf powder and JC-La 2 CoO 4 are presented in Fig. 4. In the FTIR spectra shows significant peaks and wavenumbers and an interpretation of the possible functional groups.It also proofs the phytochemicals or functional groups in the JC leaf and are responsible for reducing and stabilizing the JC-La 2 CoO 4 NPs.The characteristic stretching band appear at 500 cm -1 indicated the formation of La-O nanoparticles 48,49 .The band assigned at 668 cm -1 to the bridging vibration of O-Co-O bands 6,18 2.

SEM and EDAX analysis of the JC-La 2 CoO 4 NPs
The surface morphology of the prepared nanoparticles was examined using SEM analysis.Energy dispersive X-spectroscopy (EDAX) to identify the existing elements in the composite.Figure 5a-c

XPS analysis of the JC-La 2 CoO 4 NPs
Surface oxidation state and chemistry of La and Co ions in JC-La 2 CoO 4 were further investigated by using the core-level and satellite X-ray photoelectron spectroscopy (XPS).The binding energy (eV) and features of Co2p, La3d and O1s spectra shown in Fig. 6. Figure 6a display the hole spectra of JC-La 2 CoO 4 and assign the signals   51,52 .At the XPS spectra of JC-La 2 CoO 4 , the core-level signals of Co 2+ ions show in higher binding energy site more intense XPS signals relative to those of Co 3+ ions, and a highintensity peak of metallic Co appears at ~ 777.8 eV suggest + 2 oxidation state [53][54][55] .Which support the binding energy of O is located in 530.4 eV and valency is O1s shown in Fig. 6d.Therefore, the XPS spectra supported and conclude that the probable composition is JC-La 2 CoO 4, which satisfied the valency and total charges are balanced in the composition.

Optical properties
The UV-visible spectrum of the JC-La 2 CoO 4 is displayed in Fig. 7.The interaction of the JC-La 2 CoO 4 the band edge appearing in UV-visible spectrum at 270 and 338 nm.The optical absorption study of the JC-La 2 CoO 4 NPs revealing that electronic transition, band gap energy and luminescent property 11,56 .Band gap energy was calculated by using Tauc's relation (Eq.1).where α: represents the absorption coefficient, A: is a constant, E g : is showing optical band gap, n: is exponent that depends on transition, h: is symbol of plank\rsquo s constant The optical energy band gap energy of JC-La 2 CoO 4 is 4.95 eV calculated from Fig. 8, which appears through extrapolating the linear portion of the curve to (αhʋ) 2 = 0 and indicates its semiconductor properties and support the study of catalytic activity.Indirect band gap value is also calculated and showing in Figure S1.

Photocatalytic activity
Photocatalytic experiments were conducted using JC-La 2 CoO 4 NPs in presence of sunlight aqueous solution of different dyes like NO, MB, MO and RhB.The reactions were performed by adding JC-La 2 CoO 4 (0.1 g) into each set of a 20 mL solution of MB (3 mg/L) dyes.Before the degradation process solution agitated in the dark for 15 mint to established adsorption/desorption time is 20 mint to achieve equilibrium between MB solution and nanoparticle.The most prominent result was found in case of MB, which is faster degraded compared to others dyes with small time is shown in Fig. 8a.The degradation of MB in presence of JC-La 2 CoO 4 NPs was examined by UV-VIS spectrophotometer (UV-1800, Shimadzu) after 10 min interval shown in Fig. 8b.The initial absorbance of MB is about 0.712 at 662 nm and it takes 115 min for complete degradation after that the degradation of MB is almost constant.The rate constant of JC-La 2 CoO 4 is 56.73 × 10 -3 after 50% degradation of MB with respect to irradiation time.Therefore, JC-La 2 CoO 4 NPs shows good catalytic activity against MB compared to other dyes.The probable mechanism for degradation of MB is shown in Fig. 9.It interprets that in presence of sunlight JC-La 2 CoO 4 was activated by absorbing specific wavelength of sun light and creates electron/hole pair in the valance band.This electron is move from valance band to conduction band and generate hole pair in the ) and hydroxyl (•OH) radical was formed from oxygen and water molecule and finally MB degraded into CO 2 and water.UV-Vis.Spectra of MO, NO, and RhB shows in Figure S2 and dye degradation efficiency of MB, RhB NO and MO, summarize in the Table S1.

Effect of Catalytic dosage and initial concentration of dye on the dye degradation
For catalytic efficiency and to avoid the wasting of photocatalyst, it's necessary to optimize the amount of catalyst in the photocatalytic degradation process.The effect of the catalyst dosage of JC-La 2 CoO 4 was investigated in the degradation of MB using 0.025 g,0.05 g, 0.1 g and 0.2 g of catalyst for 115 min, which is shown in Fig. 10a.The degradation of MB dye increased as the quantity of catalyst increased from 0.025 to 0.2 g. which is shown in Fig. 10 b.As the amount of catalyst dose increased, the amount of adsorbed dye on the surface of the catalyst increased.Now the adsorbed dye molecule promptly reacts with ROS (reactive oxygen species) [57][58][59] .In the present study increased the catalyst dosage from 0.025, 0.05, 0.1, and 0.2 g/20 mL, the degradation percentage of MB dye initially increased which may be attributed to the active ROS sites generation.But in higher dosage of catalyst 0.2 g degradation percentage of MB dye decrease, and it could be due to the decrease in photon penetration on the catalyst surface block in solution which leads to a decrease the formation of ROS 60 .
The effect of the initial dye concentration of MB on the dye degradation efficiency was studying in presence of catalysts.The concentration of dye varying from 3 to 8 mg L -1 with 0.1 g photocatalyst JC-La 2 CoO 4 and percent degradation is shown in Fig. 11.
Figure 11 shows the effect of the dye concentration on the performance of the photocatalyst.The rate of photocatalytic degradation decreases from 76 to 33%.This degradation percentage occurred with an increase in dye concentration because dye concentration blocks the surface-active sites of photocatalyst, inhibiting the process for ROS generation and turn decreasing the degradation efficiency 61,62 .The maximum degradation efficiency was found in the 3 mg/L -1 solution of MB, and therefore MB dye was chosen as the optimum concentration for further degradation process.

Effect of pH on dye degradation efficiency
The effect of the pH on the photocatalytic degradation of MB dye was investigated in the presence of JC-La 2 CoO 4 photocatalyst in sunlight which is shown in Fig. 12a.The pH of the reaction from pH = 4, 7 and 9. Adjustment of pH with in the above range by using 0.1 M solution of HCl and NaOH.JC-La 2 CoO 4 photocatalyst giving better catalytic activity at pH 9 which is shown in Fig. 12b.As the resulting value nearly same at pH 4,7,9 is more favorable for the degradation of MB dye 54,63 .

The Effect of active species scavenger test
To evaluate and understand the active species, i.e., (O 2 •− )(superoxide), h + (holes), and ˙OH (hydroxyl ion) were used to study the photocatalysis mechanism which is shown in Fig. 13.For this purpose, isopropyl alcohol (IPA,1 mM) was used as ˙OH, ascorbic acid (AA, 1 mM) used for trapping 2 (O 2 •− ) and ammonium oxalate (AO, 1 mM) used as a h + scavenger.In the absence of any active species degradation rate of MB was 79%.With the addition of IPA, AA, AO degradation of MB was decrease about 35%,12%,4% respectively.The addition of all the species contribute to the degradation of MB dye.The rate of degradation in presence of IPA and AA rate is highest, therefore the ˙OH, and O 2 -species play a key role for the degradation 60,64,65 .

Recyclability and stability of the JC-La 2 CoO 4
Recyclability and stability is an important factor after the degradation process, for this prediction photocatalyst was investigated for reusability by subjecting it to three consecutive experiment cycle under the same condition up to 115 min.Figure 14 attribute to the effect of reusability test to MB degradation, the first two test efficiency rate of degradation nearly the same (77% to 75%).During the third test degradation rate 69%.The Reduction in degradation efficiency it might be due to the loss of photocatalyst in each cycle and active site blockage 19,66 .
The stability of the reused photocatalyst after repeated cycle was characterized by XRD pattern of JC-La 2 CoO 4 , which is shown in Figure S4.After the third cycle peaks showing that there is no structural change.

DC magnetic study
The DC magnetic susceptibility of the JC-La 2 CoO 4 NPs the temperature dependences χ M and χ M T are depicted in Fig. 15.Magnetic susceptibility as investigated under 10-300 K temperature and applied field is a 1000 Oe (0.1 T).The value of χ M T 32.66 cm -3 mol -1 K, this value is the contribution of Co (II) ion 4 F 9 / 2 (S = 3/2, L = 0, g = 2) and La (III) 1 S 0 (S = 0, L = 0, g = 1)(also support from XPS).Upon cooling, the value of χ M T decreases monotonically to attain a minimum value 1.55 cm 3 mol -1 K at 10.3 K, which is indicative of the existence of antiferromagnetic coupling.In the Fig. 16 as temperature decrease from 300 K, the χ M value increase, reaching a maximum 0.143 cm 3 mol -1 at 94 K and then decreases slightly reaching a value 0.138 cm 3 mol -1 at 38 K. Upon further cooling, the χ M value increase again to 0.178 cm 3 mol -1 at 10 K. Figure 17 showing the temperature dependence of 1/χ M at temperature above 195 K has been fitted by the Curie-Weiss law 4,15 .
AC magnetic study AC susceptibility (in phase and out phase) studies have been conducted for the JC-La 2 CoO 4 NPs in between 1.8 and 15 K in a zero applied field with 3.5Oe driving field to investigate for slow magnetic relaxation, i.e., SMM behaviour.The AC susceptibility studies for nanoparticles have been performed at various frequencies such as 50, 250 and 550 Hz and a plot of χ M T versus temperature (in phase and out phase) is presented in Fig. 18a and b.
The ac-in-phase susceptibility of naoparticles are in good agreement with the dc data at the same temperature.χ M ' T value is significantly increased with increasing the temperature, having a maximum value of 0.0054 cm 3 Kmol -1 at 300 K (Fig. 18a).The frequency dependent rise in the out-of-phase susceptibility is observed as a peak tail, indicating nanoparticles displays behaviour characteristic of a SMM (Fig. 18b and Table S2) 67 .www.nature.com/scientificreports/

Novelty of the work
In the past, researchers have synthesized La 2 CoO 4 using various methods, including Spray Flame and Sol-gel techniques 68,69 .However, our research marks the first instance of synthesizing La 2 CoO 4 by using environmentally friendly, green methods.While other research groups have focused on producing nanoparticles of cobalt (Co) and lanthanum (La), by sol-gel or other approach.Therefore, our approach stands out due to its uniqueness.What's more, until now, no nanoparticles have exhibited the dual properties of acting as both photocatalysts and single-molecule magnets (SMMs).The literature reviews presented in the Table 3 underscore the innovative nature of our work.

Conclusion
In the summary, first time report the bimetallic magnetic JC-La 2 CoO 4 NPs was synthesized from aqueous leaves extract of Jatropha curcas through green approach and characterized by different spectroscopic technique.The JC-La 2 CoO 4 NPs was stable up to six months due to presence of both capping and reducing agent in the leaves extract to stabilize the metal nanoparticles.The leaves extract contained (-COO -, -NH 2 and -OH) groups where -OH and -NH 2 groups involved to reduction of metal ion and -COO -group strongly bind to the surface of NPs.JC-La 2 CoO 4 NPs are semiconductor materials for which it degraded the methylene blue (MB) in presence of sunlight.Both spectroscopy studies (XPS and DC Magnetic) prove the La and Co is present in + 3 and + 2 oxidation state and support the formation of La 2 CoO 4 spinel perovskite structure.JC-La 2 CoO 4 NPs have antiferromagnetic interactions and the value of C is 0.842 cm 3 K mol -1 by Currie-wises law.From DC and AC magnetic studies JC-La 2 CoO 4 NPs shows good SMM properties.JC-La 2 CoO 4 NPs may used as catalyst in organic transformation reaction.We will work on it in future.
. The bands observed at 3315, 2916, 1604 and 1047, 1311 and 781 cm -1 , respectively, for the presence of aqueous O-H, C-H, C-O, alcoholic O-H and C-Cl functional group of JC leaf powder.Simultaneously bands obtain in the JC-Co 2 LaO 4 NPs at 1609, 1316, 1072, and 794 cm -1 , corresponds to the C=O, O-H, C-O and C-Cl with good agreement and it might be responsible for the bio reduction of Co and La to the JC-Co 2 LaO 4 NPs.The comparison study of the IR band observed between JC plant extract powder and JC-Co 2 LaO 4 NPs shown in Table
were well uniform and spherical shape and (d) showing the particle size distribution of c image in red colour.The constituents of the green synthesized JC-La 2 CoO 4 NPs consist the elemental peaks for La at 4.5 keV, Co at 1 keV and O at 0.5 keV shows in Fig.5edetermined the atomic % of metals.The average grain sizes of the JC-La 2 CoO 4 NPs is 24.1 nm estimated using ImageJ software and presented the histogram in Fig.5d.The sample agglomerates of NPs with spherical shape have very fine particle prepared by green method using leaf extract of Jatropha curcas.

Figure 5 .
Figure 5. SEM image of the JC-La 2 CoO 4 NPs at different magnification (a-c) and particle size distribution of C image in red box (d) and EDAX spectra (e).

Figure 9 .
Figure 9. Probable mechanism for degradation of MB in presence of JC-La 2 CoO 4 .

Figure 12 .
Figure 12.(a) Change in the concentration of MB dye at different pH value in presence of JC-La 2 CoO 4 .(b) Changes in the degradation rate of MB dye at different pH value in presence of JC-La 2 CoO 4.

Figure 13 .
Figure 13.The role of active species on the MB photocatalytic dye degradation.

Figure 18 .
Figure 18.(a) AC Susceptibility in-phase χ' M in phase plot for the JC-La 2 CoO 4 NPs.(b) AC Susceptibility out-phase χ''M out-of-phase plot for the JC-La 2 CoO 4 NPs.

Results and discussion Green synthesis of JC-La 2 CoO 4 NPs The
greenish yellow solution of JC-La 2 CoO 4 NPs was obtained from a plant extract, Co(NO 3 ) 2 and La(NO 3 ) 3 solution.The formation of JC-La 2 CoO 4 NPs was confirmed by UV-visible spectrophotometer.From the UV-visible spectroscopy, JC-La 2 CoO 4 NPs have an absorption peak appears at 270 and 338 nm whereas no peaks observed in the mentioned bands for Co(NO 3 ) 2 , La(NO 3 ) 3, and Jatropha curcas extract solution shown in Fig.2.Co(NO 3 ) 2 and La(NO 3 ) 3 solution absorption band was found at 300 nm.

Table 2 .
The comparison study of the IR band observed in JC plant extract and JC-La 2 CoO 4 NPs. JC-