Arc Discharge Synthesis of Chitosan‐Mediated Copper Nanoparticles for Heterogeneous Catalysis in 4‐Nitrophenol Degradation

Copper nanoparticles (Cu‐NPs) have garnered substantial interest in the field of nanotechnology due to their exceptional physical and chemical properties and cost‐effectiveness. However, challenges such as particle aggregation and rapid copper oxidation affect nanoscale production. This study systematically investigates the synthesis of colloidal Cu‐NPs using chitosan (Cts) as a stabilizer and reducing agent in the arc discharge system, comparing it to distilled water as a medium. Confirmation of the purity, size, and morphology of the Cu‐NPs is achieved through various physicochemical characterization methods. X‐ray diffraction patterns confirm the synthesis of highly pure face‐centered cubic (fcc) crystal Cu‐NPs. UV–vis analysis reveals absorption peaks at 572–585 nm, indicating pure copper. Fourier‐transform infrared spectroscopy shows peaks at 638 and 597 cm−1, corresponding to Cu─Cts bonds. Transmission electron microscopy images depict spherical nanoparticles ranging from 15 to 45 nm, with smaller sizes at higher Cts concentrations. The catalytic activity of Cu‐NPs in the degradation of 4‐nitrophenol to 4‐aminophenol is assessed, with Cu‐NPs synthesized in distilled water demonstrating superior catalytic properties compared to 0.10 wt.% Cts. This study highlights the efficacy of the arc discharge method in producing pure, uniformly sized Cu‐NPs with potential applications in catalysis.


Introduction
Nanotechnology is an important research field concerning the manipulation and design of small particles, called nanoparticles including particles in the range of 100 nm down to 2 nm where the properties are scalable with size and particles smaller than 2 nm in the non-scalable size regime. [1,2]The controlled fabrication of nanoparticles has brought nanotechnology into one of the most promising and popular fields of scientific research. [3]ue to their inherent qualities and numerous potential applications in fields such as photochemical catalysis, biosensing, gas sensors, electrochemical sensing, and energy conversion, copper nanoparticles (Cu-NPs) have received growing attention in recent years among other metal nanoparticles. [4]Currently, developed synthesis methods for Cu-NPs include chemical reduction, [5,6] thermal decomposition, [7] polyol, [8] laser ablation, [9] electron beam irradiation, [10] and an in-situ chemical synthetic route. [11]Chemical reduction is the most popular technique among these because it is straightforward, affordable, and capable of improving size and size distribution control through the modification of experimental parameters.Recently, the arc discharge technique, a new physical method for creating valuable metal nanoparticles like copper, silver, and gold, has attracted the interest of scientists and businesses. [12]This costeffective method produces uniform metal nanocolloids in both gaseous and liquid mediums.
The common types of gases employed in this technique are hydrogen (H 2 ) and nitrogen (N 2 ), [13,14] and distilled water is the common liquid. [15,16]To produce colloidal nanoparticles, the arc discharge technique in a liquid medium is employed. [17]However, the concern regarding the employment of this technique in producing metal nanoparticles is the factors affecting the size of nanoparticles produced, which are the amount of current employed, [18] and the temperature of the medium. [19]herefore, the employment of stabilizers or reducing agents such as ethylene glycol, [20] sodium borohydride, [21] and polyvinyl alcohol, [22] may proceed with the synthesis of monodispersed nanoparticles and curb the formation of agglomerations.The rise of chitosan (Cts) as a functional biopolymer-reducing agent and stabilizer has received attention in many types of research and studies of nanoparticle production.Due to the large presence of free amino and hydroxyl groups in the polymer chain, Cts is found to be one of the most versatile materials to be studied, because of its ability in performing a wide variety of modifications, [23] as well as playing the role of a reducing agent or a stabilizer.
The amount of Cts solution used plays a critical role in determining the size and stability of Cu-NPs.A higher concentration of Cts solution generally results in smaller Cu-NPs.This is because Cts molecules effectively coat the Cu-NPs, hindering collisions and mergers.Additionally, the steric hindrance provided by the Cts chains impedes the growth of Cu-NPs, leading to a more uniform size distribution.The positively charged Cts molecules electrostatically interact with the negatively charged Cu-NPs, creating a stable dispersion that prevents Cu-NPs sedimentation and aggregation.This stability is essential for maintaining the catalytic activity of Cu-NPs, as aggregated Cu-NPs have reduced surface area and accessibility to reactants. [24]ue to their thermal conductivity and high surface area to volume ratio, [25] metal nanoparticles such as copper can play an important role as a catalyst for organic alterations, which include hydration of unsaturated organic molecules, hydrogenation, and hydroxylation. [26]In nano size, copper is seen to possess an enhancement of properties which makes it entirely different from the corresponding bulk material. [27]In numerous researches on pollution reduction, Cu-NPs have been shown to contribute significantly as a heterogeneous reusable catalyst. [28,29]hen attached to a matrix, the catalytic performance of these nanoparticles can be enhanced compared to their bulk counterparts.This is attributed to the enhanced accessibility of surface atoms and a low coordination number, particularly advantageous in water treatment applications. [30]Interporous Cu alloy nanocages derived from core-shell Cu@Ni nanocubes exhibit exceptional catalytic power, especially in the hydrogen evolution reaction.Their innovative design combines copper and nickel within a hollow structure, enhancing catalytic activity and stability.These alloy nanocages with their increased surface area and efficient mass transfer capabilities represent a promising avenue for sustainable energy applications. [31]itroaromatic compounds are considered the most toxic and refractory pollutants among several known water pollutants, of which the permissible range is as low as 1 to 20 ppb. [30]Accordingly, their industrial production is considered as an environmental hazard. [32]Upon being released into the environment, these nitrophenols pose significant public health issues by exhibiting carcinogenic and mutagenic potential in humans. [33]ormally, it takes a long time for the degradation of nitrophenols in water which poses a considerable risk if it seeps into aquifers along with the groundwater. [30]These nitrophenols tend to accumulate in a deep soil and stay there indefinitely.Although several water treatment methods such as chemical precipitation, ion exchange adsorption, filtration, and membrane systems are available, they are typically slow and non-destructive.Hence, efficient catalytic removal of these highly toxic compounds is highly desirable.Generally, nanoparticles are immobilized onto supporting materials like silica, zeolites, resins, alumina, microgels, and latex which are inert to the reactants and provide a rigid framework to the nanoparticles. [34]he research aims to investigate the synthesis of colloidal Cu-NPs mediated in Cts through the arc discharge technique and compare it with NPs generated in distilled water.The primary objectives are to analyze the influence of stabilizers and reducing agents in the production process to mitigate issues such as particle aggregation and rapid Cu oxidation at the nanoscale.The study also seeks to characterize the purity, size, and morphology of the synthesized Cu-NPs using various techniques such as UV-vis spectroscopy, x-ray diffraction, Fourier-transform infrared spectroscopy, and transmission electron microscopy.Furthermore, the research explores the heterogeneous catalytic activity of Cu-NPs in the degradation of 4-nitrophenol (4-NP) to 4aminophenol (4-AP) in the presence of sodium borohydride as a reducing agent.Ultimately, the research aims to demonstrate the suitability and effectiveness of the arc discharge-synthesized Cu-NPs mediated in Cts for potential applications in catalysis fields.

Results and Discussion
The arc discharge is initiated between the two electrodes used.In the present study, pure copper was employed as both anode and cathode to produce pure Cu-NPs.The current induced between both electrodes created a thermal plasma of high temperature, which may exceed 3750 K. [35] The copper electrodes were heated by high-temperature arc plasma surrounding and this caused the copper atoms to be separated from the metal surface and evaporated into metal vapors.The metal vapors were cooled and condensed, [35] in the water to create supersaturated copper and lead to the formation of stable primary particles Cu-NPs through nucleation mechanism.This proposed a mechanism for the arc discharge system, as shown in Figure 1a.
During the arc process, gas bubbles were noticeably formed in the water caused by the occurrence of plasma vaporization/decomposition of the copper anode and water medium. [36]he formation of gaseous hydrogen and oxygen from the decomposition (electrolysis) of water interacted with the synthesized Cu-NPs. [36]Atomic oxygen was expected to be saturated with the negatively charged surfaces of Cu-NPs which were negatively  induced by electron released from cathode during the arc discharge process. [37,38]Therefore, this created hydrogen bonds of Cu-NPs in a water environment as proposed in Figure 1b.The negatively charged Cu-NPs surrounded by water molecules can create a stable suspension.

Formation of Colloidal Copper Nanoparticles
The observation of synthesized colloidal Cu-NPs is shown in Figure 2. The Cu-NPs synthesized in distilled water showed a brownish-black color in the solution.When the concentration of Cts increased from 0.025 to 0.10 wt.%, the color of colloidal solutions changed.The colloidal solution of Cu-NPs turned into light brownish red, red-brown, and dark red, respectively.The observed color change of the colloidal solution serves as a sensitive indicator for increasing Cu-NP concentration, which is directly proportional to the increasing concentration of Cts.As more Cts molecules are introduced, the color of the solution deepens, reflecting the enhanced concentration of Cu-NPs.This colorimetric approach offers a convenient and reliable method for monitoring Cu-NP concentration and assessing the effectiveness of Cts in the synthesis process.

UV-Vis Spectroscopy Analysis
As a stabilizer and capping agent, Cts is equipped with the ability to form a layer around the surfaces of Cu-NPs and provide a boundary.This layer of Cts fragments gave protection to the NPs against agglomeration and oxidation, [39] and thus, promoted the formation of pure Cu-NPs.In proving the statements discussed earlier, the production of pure colloidal Cu-NPs was analyzed and confirmed by UV-vis spectroscopy in the range of 220-800 nm.The resulting UV-vis for samples of synthesized Cu-NPs in and in different concentrations of Cts solution (0.025, 0.05, 0.10 wt.% Cts) are shown in Figure 2. The samples exhibit surface plasma resonance (SPR) absorption peaks around 572-585 nm, generally proving the formation of pure Cu-NPs. [40,41]The observed peaks in Figure 2b-d showed the features of interaction between Cu-NPs and Cts, which were previously known to show absorbance peak within the range of 500-600 nm. [42]The observed sharper absorbance peaks and blue shifting indicate a reduction in the size of the synthesized Cu-NPs with the rising concentration of Cts solution used.
Based on Figure 2b-d, the absorbance peak of the samples increased simultaneously with the increasing concentration of Cts solution used (0.025 to 0.10 wt.%).These results suggested the increasing number of Cu-NPs formed with increasing stabilizer concentrations, with 0.10 wt.% Cts solution to have the smallest synthesized nanoparticles.The highest SPR absorbance peak at the highest Cts concentration showed the effectiveness of Cts as a stabilizer and capping agent in inducing greater dispersion of the nanoparticles. [43]

X-Ray Diffraction (XRD) Analysis
The synthesis of pure and crystalline colloidal Cu-NPs was confirmed by using X-ray diffraction (XRD) analysis.The analysis reveals peaks displayed in Figure 3a for Cu-NPs in distilled water and Figure 3b for Cu-NPs in a 0.10 wt.% Cts solution.Both  220) respectively.This corresponding peak represented facecentered cubic (FCC) Cu-NPs crystals as referred to in the copper X-ray diffraction reference number (01-089-2838). [42,44]As evident from XRD results, there are no additional peaks associated with impurity compounds within the production process of Cu-NPs.As observed, the spectra in both results showed differences in intensity.The intensity of XRD peaks for Cu-NPs in Cts is lower compared to Cu-NPs in distilled water.This indicated the interactions between synthesized Cu nanoparticles with the stabilizing medium and formed a much smaller size of nanoparticles as compared to samples of Cu-NPs in water only.

Fourier Transform Infrared Spectroscopy Analysis (FTIR)
The molecular interactions between Cts medium and synthesized Cu-NPs, as well as for distilled water with Cu-NPs were studied through FTIR spectra as an additional confirmatory test.Figure 4a-d shows the spectra of pure Cts and the Ctsmediated Cu-NPs in different Cts concentrations (0.025, 0.05, and 0.10 wt.%). Figure 4e illustrates the FTIR spectrum for Cu-NPs synthesized in distilled water.The spectra for Cts showed vibration bands at 3354 cm −1 , which may be contributed by the overlapping of hydroxide (O─H) and amine (N─H) stretching bands; the peaks at 2870 cm −1 indicated aliphatic C─H stretching; 1641 and 1562 cm −1 indicated N-H bending; peaks at 1433, 1361, and 1312 cm −1 indicated C-H bending; and the peak at 1035 cm −1 indicated C─O stretching. [42,45]In the case of Ctsmediated Cu-NPs, a blue shift was observed in the samples, with peaks shifting to smaller wavenumbers and a decreased intensity of peaks, such as the N-H bending peak at 1562 shifting to 1539 cm −1 , while the second peak at 1641 cm −1 was noticeably absent in all spectra.
These changes confirmed that N-H group, featured in the Cts structure, [42] capped the surfaces of Cu-NPs.In the same manner, peaks at 1361 and 1312 cm −1 were not seen.Furthermore, the appearance of new moderate-intensity peaks was observed at 638 and 597 cm −1 for Cts-mediated Cu-NPs.These peaks signified the existence of Cu-NPs, implying an interaction between the Cu-NPs and Cts.In Figure 4e, a vibration band of low intensity emerged at 3377 cm −1 , corresponding to O─H stretching bands, along with a moderately intense peak at 650 cm −1 , demonstrating the characteristics of Cu-NPs.The observed peaks indicated potential interactions between water molecules and the synthesized Cu-NPs.

Transmission Electron Microscopy Analysis
The TEM studies were conducted to observe and analyse the shapes and structural morphologies of the synthesized colloidal Cu-NPs Micrograph of synthesized colloidal Cu-NPs are shown in Figure 5a-d.The observations' results indicated that the size of Cu-NPs exhibited a reduction in value as the Cts concentration increased.Consistency was observed in these findings with other NP characterization analyses, serving as evidence for the effective role of Cts as both a stabilizer and capping agent.The size of Cu-NPs in distilled water exhibited a larger range, spanning 20 to 100 nm, with a standard deviation of 43.06 ± 16.16 nm.Subsequently, Cu-NPs in the lowest concentration of Cts (0.025 wt.%) demonstrated a slightly smaller size, ranging from 14 to 94 nm, with a standard deviation of 35.15 ± 17.48 nm.Similarly, Cu-NPs mediated in Cts with a concentration of 0.05 wt.% exhibited sizes ranging from 5 to 40 nm, and a standard deviation of 19.06 ± 9.06 nm.
The Cu-NPs mediated in Cts of the highest concentration (0.10 wt.% Cts) were observed to have the smallest particle size, ranging from 4 to 34 nm with a standard deviation of 14.62 ± 4.45 nm.Based on the histogram in Figure 5d, the size distribution of nanoparticles was observed to be higher in the sample, which later caused the low standard deviation value found.These results strengthen the applicability of Cts as a biopolymer stabilizer in controlling the size of synthesized Cu-NPs, as discussed in previous researches conducted. [42,43]

Heterogeneous Catalysis of Copper Nanoparticles in 4-Nitrophenol Degradation
The aqueous 4-NP exhibited a prominent UV-vis absorbance peak at 318 nm, which corresponded well with the absorbance value of the pure sample. [46,47]Upon the addition of sodium borohydride to reduce 4-NP, a distinct yellow color emerged, attributed to the creation of 4-NP ions, subsequently causing a red shift in the peak to 399 nm.In the following, after a minute, an intensity reduction in the peak of 4-NP was observed.Nevertheless, in the absence of Cu-NPs to serve as a catalyst and accelerate the degradation process, the observed peak remained unchanged over time (Figure 6).This reaffirmed that the reduction process did not advance in the presence of NaBH 4 as a reducing agent. [48]y transferring electrons from a reducing agent (such as NaBH 4 ) to 4-NP, Cu-NPs can function as reducing catalysts, changing 4-NP into the less toxic 4-AP.This reaction is an appealing method for treating wastewater since it usually occurs in mild circumstances.The overall reaction of this reduction process is listed below.
Commonly, aromatic compounds that contain nitro groups (−NO 2 ) are impotent to the reduction process via reducing agents like NaBH 4 . [46,49]However, with the addition of Cu-NPs as a catalyst, the vivid yellow color resulted from mixing 4-NP with NaBH 4 , faded to light yellow and reduced to a colorless solution, and peaks at 399 nm decreased with the emergence of peaks at 297 nm. [29]These changes in appearance were due to the reduction of 4-NP to 4-AP.These changes are seen for both samples used; Cu-NPs in distilled water, and Cu-NPs in 0.10 wt.% Cts solution.The employment of Cu-NPs catalyzed the reaction through electrons transfer from borohydride ions (BH 4 − ) to the nitro group attached in 4-NP and thus, reduced it to 4-AP.
Based on Figure 7a, the catalytic activity of Cu-NPs prepared in DD-water was confirmed as the peaks of 4-NP at 399 nm were reduced rapidly with period gaps of 8 min, and 4-AP peaks appeared and intensified at 297 nm, as shown in Figure 7b.The completion of the reduction process took a total of 32 min, for the 4-NP to be completely reduced to 4-AP.However, different observations were seen in Figure 7c,d, for the reduction process with the employment of Cu-NPs synthesized in 0.10 wt.% Cts.
As observed in Figure 7c, the 4-NP peaks at 399 nm were reduced slowly with period gaps of 8 min and 4-AP peaks appeared slowly with low intensity at a wavelength of 297 nm as in Figure 7d.After 72 min of the reduction process, the results showed that 4-NP was not completely reduced to 4-AP.Generally, there are many factors that affect the efficiency of the reduction process of 4-NP by the employment of metal nanoparticles such as gold, silver, and copper.Two common factors that were being discussed and analyzed in previous researches were the effect of nanoparticles size, [50][51][52] and the diffusion rate of 4-NP onto the surface of nanoparticles. [53]he factor that may induce such results was the electron transfer rate on the surface of Cu-NPs, which was influenced by such conditions of diffusion rate of 4-NP on the surfaces of Cu-NPs, electron transfer from borohydride ions (donor), to 4-NP (acceptor) and diffusion of 4-AP away from the NPs surfaces. [53,54]hese posed to the diffusion-controlled mechanism, which is associated with the presence of Cts features, forming layers and capping the surfaces of synthesized Cu-NPs. [55,56]The limited flexibility of Cts, [52] which caps and stabilizes Cu-NPs, restricts 4-NP diffusion onto the NP surface.This constraint, caused by the Cts layer, reduces the exposed surface area of the particles available for reacting with borohydride ions.Hence, this limitation diminishes the catalytic efficacy of Cu-NPs for the heterogeneous reduction of 4-NP.As a result, the reason for the difference between the results obtained from Figure 7a-d) is that, as the Cu-NPs were synthesized in distilled water, caused only the presence of water layering around the surfaces of NPs.This layer of water  Illustrates the heterogeneous catalysis of Cu-NPs in the degradation of 4-NP using NaBH 4 .In a,b), the decrease of 4-NP peaks was accompanied by the appearance of 4-AP peaks when Cu-NPs were prepared using DD-water.In a,b), the decrease of 4-NP peaks was accompanied by the appearance of 4-AP peaks when Cu-NPs were prepared using DDwater.In c,d), the reduction of 4-NP peaks coincided with the appearance of 4-AP peaks when Cu-NPs were prepared using 0.10wt.%Cts.
was much more suitable compared to Cts, which then allowed the diffusion between 4-NP and the surface of Cu-NPs, and its reduction to 4-AP will be faster.

Conclusion
The unique attributes of metallic nanoparticles, serving as electrical conductors and catalysts, have spurred significant interest in exploring Cu-NPs synthesis.Employing the arc discharge technique mediated by Cts yielded pure, monodispersed colloidal Cu-NPs.Cts emerged as an effective biopolymer stabilizer, leveraging its chelating properties to regulate NP size, as evidenced by UV-vis spectroscopy and TEM results demonstrating varied Cts concentrations synthesizing Cu-NPs of different sizes.TEM analysis recorded sizes of 43.06, 35.15, 19.06, and 14.62 nm for Cu-NPs in DD-water, 0.025, 0.05, and 0.10 wt% Cts.XRD patterns unequivocally confirmed the formation of pristine Cu-NPs, revealing distinct copper peaks devoid of impurities.Catalytic reduction experiments disclosed that the Cts layer's inflexibility around Cu-NPs, contrasting with those in DD-water, reduced the catalyst surface area, impeding efficient complete conversion of 4-NP to 4-AP within a specific timeframe.While Cu-NPs in DD-water achieved a complete reduction in 32 min, those at 0.10 wt% Cts remained incompletely reduced even after 72 min, indicating an ongoing process.Despite larger Cu-NPs in DD-water than Cts-mediated Cu-NPs, the former exhibited significantly faster 4-NP reduction rates, highlighting superior kinetics.
Preparation of Chitosan Solution: To prepare the Cts solutions of three different concentrations; 0.025, 0.05, and 0.10 wt% Cts, the Cts powder was weighed and prepared in three different masses; 0.2, 0.4, and 0.8 g respectively.In the first step, the weighed Cts powders were dissolved in 700 mL of distilled water, respectively, and stirred continuously at the temperature of 75 °C.A solution containing 1 g of 0.1 m HOAc was mixed with 100 mL of distilled water and subsequently added to the solution of dissolved Cts powders.The solution was then continuously stirred to homogenize.

Synthesis of Colloidal Copper Nanoparticles:
The equipment that will be used to perform the arc discharge process is PNC-1K Plasma Nano Colloid Maker, manufactured by PNF Co. (IR).Two high-purity copper wires (95.90%) of 5 mm in diameter and length of 35 mm are employed as a movable anode and a static cathode in our arc discharge experiments in distilled water.The distance between the two copper electrodes is set at 2 mm with a 45°angle between the two electrodes.Constant currents of 100 A were passed through water-immersed copper electrodes (5-10 millisecond).The arc discharge was initiated by slow movement of the anode from cathode terminal.Consequently, the feeding rate of copper wire as an anode was fixed at 1.3 cm −1 s to maintain a stable discharge current and average voltage of 30 V in experiments.Separating the electrodes increases the voltage while bringing the electrodes close together decreases it.The voltages and currents employed are recorded when stable discharge conditions are attained.The Cu electrodes are heated by the high temperature of the arc, and metal atoms are separated from the metal surface and evaporated into metal vapor.The cooled metal vapor in water lead to the formation of primary particles by nucleation mechanism turning into Cu-NPs dispersed in Cts dissolved in distilled water. [56,57]Gas bubbles are generated in the water during the arc process through plasma vaporization of the anode material, serving as both condensing agents and transporters for the end products to the water's surface. [56]The pace of nucleus expansion is governed by factors such as the quantity of vaporized metal, density of the Cts medium, and the medium's temperature.During the experimental phase, copper wire electrodes were submerged in Cts solutions with varying weight concentrations (0.025, 0.05, 0.10wt.%).The proper arrangement of the arc discharge technique employed is illustrated in the schematic diagram, as in Figure 8.The Cu-NPs colloid samples corresponding to various Cts concentrations were examined to investigate the characteristics of the formed Cu-NPs.This analysis also served to affirm the function of Cts as both a size controller and a stabilizer.
Characterization of Copper Nanoparticles: The successful production of colloidal Cu-NPs in distilled water and different Cts concentrations was characterized by the use of UV-vis spectroscopy through a UV-vis Spectrophotometer (UV-2600, Shimadzu) in 300-700 nm wavelength range.Clean quartz solution cells were used for the analysis of each sample.Characterization was conducted using Cu-NPs synthesized in distilled water and those within a Cts medium.Prior to placement in the UV-vis chamber, the quartz solution cells were used to homogenize all synthesized Cu-NPs samples.To evaluate the structures of crystalline Cu-NPs, powder X-ray diffraction experiments were carried out by using an XRD Spectrometer (XPert Powder XRD, Philips) at a small scale of diffraction angle ranging from 10°to 90°.Transmission electron microscopy (TEM) was carried through an electron microscope (JEM-2100, JEOL Ltd.), to analyze the morphology and size of the samples of synthesized Cu-NPs.An insight of functional groups presented in the sample formed can be confirmed from the FTIR spectroscopy.This technique is ideal for observing vibrational transitions of self-assembled functional groups coordinated to the NPs surfaces.The attenuated total reflection (ATR) method was adopted to observe the absorption peaks of Cts, as well as its interaction with Cu-NPs.The Cu-NPs from each dried sample were analyzed by using an FTIR spectrophotometer (IRTracer-100, Shimadzu).The FTIR spectrum was set to run within the range of 400 to 4000 cm −1 .
Preparation of Colloidal Cu-NPs in 4-nitrophenol Degradation: The catalytic efficiency for a heterogeneous system of Cu-NPs was studied through the model of 4-NP reduction by NaBH 4 .Both solutions, 4-NP and sodium borohydride were prepared in 0.15 and 25 mm of concentration respectively.To study the degradation process, the reduction of 4-NP peaks was observed through the analysis of UV-vis spectra in the wavelength range of 250-600 nm.Clean quartz solution cells were used for the analysis of each sample.The solution of mixed 4-NP and NaBH 4 , along with a blank sample of solvent were used to carry out the analysis.All samples of synthesized Cu-NPs were homogenized in the quartz solution cells before placed into the UV-vis chamber.The color change was qualitatively observed by taking UV-vis spectra at every 3 min interval.The maximum absorbance of 4-NP at 400 nm, was used as a characteristic to be monitored in monitoring the remaining 4-NP, the appearance of absorbance peak at 300 nm was monitored to identify the presence of 4-AP.To study the role of Cu-NPs, two different Cu-NPs, which were Cu-NPs in distilled water and Cu-NPs in 0.10 wt.% Cts were added to the system.The color changes of the solution were qualitatively monitored through analysis of UV-vis spectra every 8 min.

Figure 1 .
Figure 1.a) The arc discharge system involves Cts as a biopolymer mediator, with a b) a schematic diagram illustrating the interaction between Cu-NPs and Cts molecules.

Figure 7 .
Figure 7. Illustrates the heterogeneous catalysis of Cu-NPs in the degradation of 4-NP using NaBH 4 .In a,b), the decrease of 4-NP peaks was accompanied by the appearance of 4-AP peaks when Cu-NPs were prepared using DD-water.In a,b), the decrease of 4-NP peaks was accompanied by the appearance of 4-AP peaks when Cu-NPs were prepared using DDwater.In c,d), the reduction of 4-NP peaks coincided with the appearance of 4-AP peaks when Cu-NPs were prepared using 0.10wt.%Cts.

Figure 8 .
Figure 8. Schematic illustration of the arc discharge system experimental setup for synthesis Cu-NPs mediated in Cts as a biopolymer.