Green Synthesis of Electrochemically Active Silver Nanoparticles

The manufacturing of silver nanoparticles (AgNPs) is now safer, more economical, nontoxic, and environmentally benign thanks to the extraction of Cirsium japonicum . The extracts from C. japonicum worked as a stabiliser and reducer. AgNP synthesis was verified by UV/Vis spectroscopy. There have been studies done on the production of AgNP at various temperatures and concentrations. Their dispersion was validated by high resolution transmission electron microscopy (HRTEM), which also revealed their tiny (2–8nm) spherical form, lack of aggregation, and spherical shape. AgNPs were found to be crystalline using X-ray diffraction (XRD). Using EDX, it was possible to determine the substance's elemental makeup. FTIR spectroscopy was used to identify the chemical molecules that coat AgNPs. The photodegradation of bromo phenyl blue has been investigated in a variety of settings, including experimental setups and catalyst size and structure. In about 12 min, 98 percent of the bromo phenyl blue was destroyed using AgNPs as photo catalysts. Water purification and the transformation of organic hazardous substances into non-hazardous products are obvious uses for AgNPs due to their powerful reductive capabilities. Amazing electro-catalytic abilities for hydroquinone were shown by the electrode (Ag/GC) that was transformed to AgNPs. In an acetate buffer solution, the cyclic voltametric analysis of AgNPs was examined. The experiment findings for GC and modified AgNPs were contrasted. The conductivity of AgNPs was investigated in an acetate buffer solution with a 0.15 M concentration. The generated AgNPs are uniform in size and stability. The produced AgNPs' electrochemical potential was shown.

various kinds of bacteria adversely harm silver, as is widely known. Currently, a number of applications for silver composites with slow silver release rates are being researched 2 . Nanomaterials are increasingly being exploited as a result of their distinct physical and chemical properties 3 . Due to their peculiar optical, electrical, and catalytic capabilities, metallic nanoparticles have been the subject of recent material chemistry study. These biomolecular compounds can be coupled with a variety of useful nanomaterials, such as drugs, ligands, and antibodies with potential biological applications. The physiochemical and biological characteristics of silver-based nano products are distinct from those of other metal nanoparticles. Food, drugs, biomedical imaging, cosmetics, polymers, bactericidal and fungicidal chemicals, and food have all used it. Without a doubt, the ion discharge from the crystalline centres of silver nanoparticles increases their toxicity 6 . Catalytic processes have grown in significance as a result of expanding energy, environmental, and resource challenges 7 . Nanomaterials feature more edges, corners, and high energy than their bulk counterparts, making them more reactive. The usage of silver nanoparticles in commercial products and their discharge into the environment have drawn significant interest from the scientific and regulatory sectors. Both an old and new issue, silicon dioxide discharge into the environment 8 . Green nanoparticle syntheses are presently getting a lot of interest since they are more environmentally friendly than chemical and physical synthesis because they use non-hazardous solvents and reagents. Metal nanoparticles play a key role in nanotechnology because of their unique physical and chemical properties, such as catalytic activity and cutting-edge electrical, magnetic, and optical capabilities [9][10][11][12] .
Although many conventional techniques were used to create nanoparticles, chemical approaches were most frequently used. The hazardous chemicals used in chemical reduction techniques make nanoparticles unsuitable for biological uses. Nanoparticles' physical, chemical, and biological properties are significantly influenced by their size, shape, morphology, and dispersion. Chemical synthesis is the most common way for creating many nanoparticles quickly and with exact control over particle size distribution 15 . Biosynthetic nanopar ticles can be produced by fungi 16 , bacteria 17 , plants [18][19][20][21][22][23][24][25][26][27][28][29] , and algae 30 . Numerous industries, including electronics, catalysis, material science, biomedicine, cosmetics, phar maceuticals, environmental analysis, and remediation, heavily utilize noble metal nanoparticles (NPs) 36 . Their strong reactivity, high surface-to-volume ratio, and tunable optical characteristics are to blame for this. The ability of chemically altered electrodes to detect significant compounds is well recognized [37][38][39][40] . Different electrodes have occasionally been employed to electrochemically reduce oxygen. Both the electro catalytic oxygen reduction on plumbagin modified GCEs 44 and the pH-dependent oxygen reduction on multiwall carbon nanotube modified GCE were reported to occur at physiological pH settings. the pH-dependent oxygen reduction on multiwall carbon nanotube modified G., the electro reduction of oxygen to water at "wired" Pleurotus ostreatus laccase cathode 42 , and the electro reduction of oxygen to water at mediated Melano-Carpus Albomyces laccase cathode 41 . Using the aqueous extract of C. japanicum, the current experiment generated equally distributed AgNPs. The photocatalytic degradation of bromo phenyl blue was investigated using the recently created AgNPs. In addition, the electrochemical oxidation of hydroquinone by AgNPs derived from green materials was studied. In this study, silver nanoparticles are phytosynthesized using Cirsium japonicum, and the electrochemical properties of the electrode modified with silver nanoparticles are characterized.

preparation of Cirsium japoni cum extract
To get rid of any dust, C. japonicum was repeatedly washed in distilled water at Musa khel in Bannu, Pakistan. Using demonic water at a rate of 250 revolutions per minute for 39 min, 50 g of the dust-free plant material were extracted. After 10 min of centrifugation at 5000rpm with filter paper, the supernatant was collected and utilised. As a reducing and stabilizing agent, AgNPs were produced from the resulting clear filtrate.

Synthesis of silver nanoparticles
A 200 mL beaker containing 50 mL of a 3 103 M aqueous solution of silver nitrate and 10 mL of C was used to create AgNPs. Japaneseium aq extract. By switching from white to black in less than 80 min, AgNPs were investigated. The resulting black color is a definite indicator that AgNPs are starting to develop. The black color is visible due to the surface Plasmon resonance of the AgNPs. It was possible to watch the growth of nanoparticles using UV-Vis spectroscopy. The AgNPs suspension was repeatedly separated from the water for 20 min at 10,000rpm using centrifugation.

photo catalytic activity
Tests for photocatalytic activity were conducted using bromophenyl blue decomposition in aqueous solution. The light source was a UV-light. AgNPs were dissolved in 60 mL of bromo phenyl blue solution (15 mg/L) with the addition of 9 mg of AgNPs.

Fig. 2. EffectoftemperatureduringAgNpsformation
In addition, an AgNP-free control configuration was discovered. After 35 min of dark magnetic stirring, the working solution was in equilibrium before being exposed to radiation. As soon as the suspension was created, the bromo phenyl blue solution was placed under UV light, and the rate of deterioration was then checked every 30 min after that. At 614nm, a Shimadzu 2450 UV-V spectrophotometer was used to track the decline of BPB. The equation was used to determine the degradation percentage.

Fig. 3. XRdpatternsofthesynthesizedAgNps
While blank (control) has an absorbance of Ac, test has an absorbance of At. Using a blank test, the dye's self-degradation under visible light was also assessed.

Characterization studies
The biogenesis of silver nanoparticles was monitored using a UV-2450 spectrophotometer (Shimadzu) with a resolution of 1nm in the wavelength range of 350-800nm. The Rigaku Miniflex X-ray diffractometer was used to evaluate the XRD pattern between 10 and 70 degrees. The appearance, size, and crystal structure of Ag nanoparticles were investigated using a JEOL3010 high resolution transmission electron microscope and a Hitachi EDX elemental microanalysis equipment. The infrared (IR) spectrum of Ag nanoparticles was acquired using a transmittance mode with a resolution of four centimeters on an ABB MB3000 spectrophotometer.

Cyclic voltametric evaluation of an electrode modified with AgNPs
The glassy carbon electrode (GCE) was ultrasonically washed in methanol to create a mirror-like finish after being polished with alpha Al 2 O 3 to a 5mm diameter. The AgNPs and activated charcoal that had been dissolved in the polished GC electrode at room temperature were free of the solvent. The resultant GC/AgNPs were subsequently described. Using a disinfectant, loosely bound AgNPs were removed from the modified GC electrode. The experiment that follows made use of this modified electrode.

Voltammetry in cycles
For the cyclic voltametric analysis, the electrochemical workstations CS-300 and CHI-600 were utilized. In this measurement, 5mm-diameter glassy carbon electrodes (GCEs) and modified GCEs were used as working electrodes, Pt wires were used as a counter electrode, and saturated calomel electrodes (SCEs) were used as standards. Glassy carbon electrodes modified with AgNPs have electrocatalytic activity.
The redesigned electrode was evaluated electrochemically in an electrolyte medium with a 0.15 M sodium acetate solution (CV). In order to assess the electrocatalytic performance of biogenic AgNPs, cyclic voltammetry was performed (CV). The CV responses of the phenol catechol C 6 H 6 O 2 in 0.15 M sodium acetate solution were compared using a glassy carbon electrode (GCE) at room temperature and an AgNPs-assembled glassy carbon electrode (SCE) at room temperature. The electrochemical breakdown of BPB was studied in an aqueous sodium acetate solution using modified AgNPs as the working electrode.

RESULTS & dISCUSSION
UV-Vis spectroscopy UV/Visible spectroscopy was used to track the rate of Ag nanoparticle synthesis. Metal nanoparticle SPR patterns can be discovered using UV-Visible spectroscopy. The phenomenon known as SPR occurs when the conduction band electrons of metal nanoparticles collectively vibrate in resonance at a particular wavelength of the illuminating light. Fig. 1a demonstrates how the UV/Visible spectral monitoring was time-dependent. As shown in Fig. 1a, the SPR peak becomes more intense and sharper as contact time increases. SPR indicates that the absorbance peaked at 447nm. AgNPs' environment, size, and shape dispersion all have an impact on their SPR peak. For metallic nanoparticles between 2 and 100nm in size, SPR produces a peak that has been thoroughly investigated 45 . The effects of several plant extracts on the synthesis of AgNPs are shown in Fig. 1b. An SPR band at 430nm was discovered as soon as 10 mL of plant extract was added to the silver precursor. At this quantity of plant extract, a very low absorbance was observed, which showed that few nanoparticles had formed. However, when 20 mL of the plant extract were employed, the SPR peaks' intensities rose.

Effect of temperature on their action rate
The AgNPs were heated to different temperatures before having their surface plasmon resonance spectra collected, as seen in Fig. 2. The peak's sharpness increased from 20 to 40°C, suggesting that there may have been an increase in reaction time. The produced nanoparticles' small size is what causes the peak to be so sharp 48 . If the extract's reducing and stabilising power is diminished when heated above 80°C, it may only have a limited capacity to stabilise at higher temperatures. It is conceivable that organic Compounds break down at temperatures below 100°C since the majority of organic substances are stable there. the diagram of X-ray diffraction.

X-ray diffraction (XRd) pattern
As shown in Fig. 3, XRD analysis was used to determine the crystal structure of the synthesized AgNPs. The Bragg reflection peaks of 38.21°, 44.30°, 64.52°, and 77.47° of face-centered cubic silver, respectively, indicate the 111, 200, 220, and 311 lattice planes. The observation at 2=38.21 is in agreement with the cubic AgNPs with faces 49 , shows a significant peak. The findings of this study show that the 111 plane is the top crystal plane (basal plane) in the creation of nanoparticles. Due to its high atomic density, the 111 facet is regarded to be the most reactive. Silver and gold nanoparticles have previously been shown to exhibit a similar diffraction pattern when reduced and covered with plant extract 50 . The following Debye-Eq. Scherrer's law illustrates how the FWHM (full width half maximum) of the diffraction peaks was also used to determine the typical crystal size of these particles. The Scherrer's constant in this instance is d14K=cos K. is the ray's X-wavelength. The symbols for the Braggs' angle and the half-breadth of the peak are and, respectively.

X-ray with energy dispersion (EdX)
The EDX profile, which displayed substantial signals in the 3 keV range and is a characteristic signal for the absorption of metallic and spherical nano crystals due to surface plasmon resonance 51,52 , corroborated the elemental composition of silver nano crystals. A high silver nanoparticle yield was achieved because there was no longer any ionic silver (Ag + ) signal, indicating that all of the Ag + had been transformed to Ag°. FT-IR analysis and EDX patterns demonstrate that C. japonicum extract is Scheme 2. diagrammatic depiction of silver nanoparticle formation The particle size might grow even larger if the plant concentration was raised further. An increase in the polyphenolic content may account for the larger particle size observed at higher plant concentrations. According to earlier research, these molecules are necessary for the production of nanoparticles 46 . Everything here indicates an increase in the production of silver nanoparticles with a restricted size distribution. used to decrease silver ions and produce crystalline AgNPs. The functional groups responsible for the reduction and capture processes have been located in the aqueous extract of C. japonicum using FT-IR analysis. Aqueous extracts of C. japonicum and silver nanoparticles produced by C. japonicum are shown in Fig. 5. The infrared spectra at the following wavelengths, in that order: 3355 cm -1 , 2930 cm -1 , 2930 cm -1 , 2355 cm -1 , and 3355 cm -1 , reveal one of the most notable properties of the C. japonicum aqueous extract. The -OH stretching-related vibrational peaks are located at 3355 cm -1 . As far as we can tell, amide II's NH stretching vibration, as well as the C-O stretch and C-N stretch, are contained in the extra peaks at 2930, 1385, and 1083 cm -1 . An apparent decrease in peak intensities in the FT-IR spectra of AgNPs produced by C. Japanicum suggests that these groups may be involved in the synthesis and stability of AgNPs. The flavonoids' -C O stretching vibration decreased from 1640 to 1670 cm -1 , the AgNPs' O-H stretching vibration increased from 3355 to 3499 cm -1 , and amid II's NH stretching vibration increased from 2922 to 2921 cm -1 54-55 .

Scheme 3. Mechanism of photo degradation of bromophenylblue (BpB)byAgNps
These findings suggest that a number of functional groups, including proteins, flavonoids, and saponins, present in the phenolic components of the Japani cum aqueous extract, may stabilize the AgNPs generated. These alcoholic chemicals' hydroxyl groups may support silver's bio-reduction. The FT-IR spectrum of Fig. 5 shows that -OH groups, which are present in Cirsium species 56 , are essential for the synthesis and stabilization of AgNPs. It has been proposed 51,52 to employ C. japonicum extract as a reducing and stabilizing agent for the manufacture of AgNPs. Schemes 1 show the proposed process for making AgNPs.

High resolution transmission electro n microscopy
Using HRTEM, the produced AgNPs' size, shape, mor phology, and dispersion were all studied. The morphology of the silver nanoparticles matches the form of the SPR band in the UV-Vis spectrum, which is perfectly visible in the HRTEM image. The estimated particle size from the XRD analysis and the average particle size from the HRTEM images, which ranges from 4 to 8nm, are well matched. Fig. 6 shows the spherical and highly dispersed AgNPs, and the HRTEM findings, which are consistent with the EDX results, show no signs of aggregate formation. Because of their large surface area, increased number of active sites, smaller, spherical particle size, and good dispersion, AgNPs exhibit excellent electrocatalytic and photocatalytic activities 57,58 .

photo degradation of bromophenylblue (BpB)
For the sake of the environment, AgNPs' photocatalytic efficiency must be increased.
Numerous industries pollute the environment with dye and other organic substances, putting people, plants, and animals in peril. The breakdown of BPB, one of the colouring agents, necessitates a number of circumstances because it is a stable organic chemical with a big aromatic molecular structure that is particularly resistant to heat and light. Since BPB has such a negative impact on the environment, scientists must do critical research on this topic and address a significant problem. Nanoparticles are extremely valuable for degrading these waste products. In this experiment, the photo catalytic activity of AgNPs was assessed using the model compound bromo phenyl blue. The degradation of photographs was assessed using bromo phenyl blue, which demonstrated a distinct absorption peak at 630 nanometers. The examination of the absor ption spectra of BPB aqueous solutions over time in the presence of AgNPs is depicted in Fig. 7a and 7b. In the presence of AgNPs and light, it was observed that the main absorption peak shrank, indicating photodegradation of BPB. AgNPs have a stronger photodegradation property for three reasons. The first justification is that AgNPs do a superior job of light absorption. Due to their small size, silver particles have more active sites and can cover a bigger surface area. The third cause is high dispersion without any agglomeration. Particle morphology, crystal structure, and size all significantly affect photo catalytic activity, according to studies 59,60 . The mechanism that has been postulated up to this point is shown in Scheme 3 and involves AgNPs breaking down BPB photocatalytically. The idea was that when the AgNPs were exposed to UV light, the valence electrons in their valence shell would be freed. These more powerful electrons produce hydroxyl radicals, hastening the breakdown of BPB. AgNPs concentrations and temperature effects.
The photodegradation of bromo phenyl blue was examined by increasing the concentration of AgNPs in the solution from 5 to 10 mg, as shown in Fig. 8a. The outcomes are displayed in UV radiation was used in this experiment for 20 min at room temperature (see inset in Fig. 8a). The breakdown of bromo phenyl blue increased from 80% to 98% when the amount of AgNPs was increased from 5 to 10 mg. From 15 to 20 mg of AgNPs, the efficiency of AgNPs' photodegradation decreased, showing that AgNPs' capacity for photodegradation decreased with concentration. Smaller, scattered particles provide more surface area and active sites for AgNPs' photodegradation against BPB at lower concentrations than larger, dispersed particles. Between 5 mg and 10 mg, the photodegradation activity of the AgNPs significantly decreased. The agglomeration of AgNPs at higher concentrations, which increased particle size, resulted in a decrease in the specific surface area of the particles and the number of surface-active sites. The highest photodegradation efficiency for bromo phenyl blue was found to be 10 mg of AgNPs. As seen in Fig. 8b, temperature has an effect on BPB photodegradation. The degradation of BPB is directly influenced by temperature. At 30°C, only 15% of BPB was degraded; at 50°C, breakdown reached 98%. The degradation of BPB by the AgNPs was discovered to be more significant than their paralyzing effect, as seen in Figure 8b.
Electro chemical behavior of catecholatAg-Nps modified electrode U t i l i z i n g c y c l i c vo l t a m m e t r y, t h e electrocatalytic activity of biosynthesised AgNPs was evaluated. Fig. 9a shows the catechol C 6 H 6 O 2 CV responses at the glassy carbon electrode (GCE), in contrast to the saturated calomel electrode (SCE). Anodic and cathodic peaks in Fig. 9a have similar intensities. [61][62][63][64][65][66] This states that the electrolytically produced highly reactive species qunonine (2a) is oxidized to catechol. This highly reactive species' stability on an electrode surface was also shown by the redox pair [64][65][66] . Catechol-modified AgNPs were studied using multi-cycle cyclic voltammetry in a 0.15 M sodium acetate electrolyte. The anodic peaks at 0.1, 0.45, and 0.53 V slightly lost power during the circular scanning [65][66][67][68] . "a," which occurred at a lower voltage, demonstrated the stability of the o-qunonine produced during the electrochemical oxidation of catechol.

Effect of linear weep potential of modified paste vs SCE at 25°C
Because of the equilibrium between 1a and 2a, as shown in Fig. 9b, the peak appeared to be declining with lower scanning. Two anodic peaks (A and A1) are observed during the electrochemical oxidation of phenolic compounds, proving that the process is a 2e, reversible one 67,68 . Scheme 3 66 shows both the anodic conversion of catechol to o-qunonine and the reverse conversion of qunonine to catechol. There was no difference in peak intensity between the second and third cycle because, as Scheme 4 illustrates, the equilibrium between 1a and 2a had been reached. The electrochemical oxidation of catechol to o-quinine provided the best sensitivity for the GC-modified electrode, as can be seen in Figure 9b.

deprivation of bromophenylblue by electro chemical method using glassy carbon-AgNps modified electrode
Cyclic voltametric analysis in aqueous media with a 0.15 M acetate buffer solution was used to evaluate the degradation of BPB 53 using the modified GC/AgNPs electrode shown in Fig. 10. When heated to 25°C and scanned at speeds between 100 and 80 mV/s -1 , BPB liquefied more quickly than SCE (as depicted in Fig. 10a). The BPB showed two anodic peaks and one cathodic peak at different potentials when scanning more quickly (A, A1 and C). During electrochemical reactions in aqueous conditions, an additional "a°" peak appeared at 0.3 V, proving the stability of the produced intermediate. The electrochemical reaction resulted in three C peaks at 2.5, 4.2, and 0.7 V, two anodic and one cathodic. Anodic peaks (A and A1) are produced by the cathodic peak (C), which represents the opposite process, and require a higher voltage than those produced by the intermediate oxidation shown in curve. This is brought on by the intermediate's stability in an aquatic setting. The redox process in IpA/IpC is analogous to that in electrochemical processes [61][62][63][64][65][66][67][68] . Slower scanning rates reduce the anodic and cathodic peaks because BPB concentration is reduced as BPB is electrochemically broken down. It is shown that the potential of Peak A2 is higher while scanning at a rate of 20 mV/s -1 . At a scanning rate of 20 mV/s -1 , the BPBs seem to be completely degraded to their corresponding products. A2 may be produced by electrochemical techniques such as polymerization or hydroxylation 65 . Scheme 5 displays the anticipated electrochemical breakdown of BPB.

CONCLUSION
Using C. japonicum extract as a reductor and stabilizer, a bio-green technique that is costeffective and ecologically friendly was used to create the well dispersed, stable, and electrochemically active AgNPs. The plant extract can be used to make nanoparticles with particular sizes and morphologies. By using XRD and EDX, the AgNPs' FCC structure and elemental composition were confirmed. The HRTEM results showed that the AgNPs were tiny, spherical, and broadly distributed at low plant extract concentrations. Ag-NP produced through biosynthesis has different diameters depending on the reaction duration. As a result, Ag-NP size increases at room temperature as reaction time increases. Silver nanoparticles have been found to be highly effective and sensitive electrocatalysts. In other words, the redox process and other phenolic applications benefit from the electrocatalytic capabilities of Ag/GC. This process may generate AgNPs without the use of any dangerous chemicals, making it appropriate for electrochemical and medicinal applications. The BPB was successfully removed from water by the synthetic AgNPs. To better understand how BPB and other colours (organic pollutants) are electrochemically broken down by AgNPs during water filtration, more research is urgently required.

ACkNOwLEdGEMENT
Authors are thankful to Head, Department of Chemistry, A.V.V.M. Sri Pushpam College (Autonomous) for providing lab facilities.