Green Synthesis of Cu Nanoparticles in Modulating the Reactivity of Amine-Functionalized Composite Materials towards Cross-Coupling Reactions

Control over both dispersion and the particle size distribution of supported metal particles is of paramount importance for the catalytic activity of composite materials. We describe the synthesis of materials with Cu nanoparticles well-dispersed on different amine-functionalized supports, using the extract of Wallich Spurge as a green, reducing agent. Graphene oxide (GO), mesoporous silica (MCM-41), mesoporous zirconia, and reduced graphene oxide-mesoporous silica (RGO-MCM-41) were explored as supports. Cu nanoparticles were better stabilized on RGO-MCM-41 compared to other supports. The novel composite materials were characterized by X-ray diffraction (XRD), Raman spectra, Scanning electron microscope (SEM), Transmission electron microscopy analysis and HR-TEM. SEM and EDX techniques. High angle XRD confirmed the conversion of graphene oxide to reduced graphene oxide (RGO) with plant extract as a reducing agent. Both XRD and TEM techniques confirmed the Cu nanoparticle formation. The catalytic activity of all the prepared materials for the Ullmann coupling reactions of carbon-, oxygen-, and nitrogen-containing nucleophiles with iodobenzene was evaluated. From the results, 5 wt% Cu on amine-functionalized reduced graphene oxide/mesoporous silica nanocomposite (5 wt%Cu(0)-AAPTMS@RGO-MCM-41) exhibited excellent efficiency with 97% yield of the C-C coupling product in water at 80 °C in 5 h. The activity remained unaltered almost up to the fourth cycle. The Cu nanoparticles stabilized by organic amine group on RGO hybrid facilitated sustained activity.


Introduction
The distinct properties of nanoparticles activity were well explored and harvested in different chemical manufacturing fields, biological applications, energy conversion, hydrogen production and storage, and environmental technology [1][2][3][4]. Due to unique shapes and sizes, the metal nanoparticles exhibit better catalytic activity than their bulk materials. The nanoparticles of precious metals such as gold, palladium, and silver have been well explored in various applications [5][6][7][8][9]. Generally, nanomaterials are expensive, toxic and unstable. Hence, stable nanomaterials prepared using inexpensive metals and abundant sources as reducing agents are economical and attractive [5]. Thus, Cu nanoparticles are appealing because of their high natural abundance and low cost [10,11]. Cu with different oxidation states (Cu 0 , Cu I , Cu II , and Cu III ) can be oxidized and reduced easily [12]. Thus, Cu nanomaterials can promote various reactions for energy, environmental and industrial requirements.
Carbon-based materials, including graphene, carbon nanotube, fullerene, have received significant attention as support materials for loading different nanoparticles. The

Preparation of Leaf Extract Reducing Agent
In the leaf extract preparation, dried leaf powder of Wallich Spurge (50 g) was added to distilled water (200 mL) followed by constant stirring for 2 h at 80 • C. Then, the mixture was centrifuged for 10 min and filtered, and the filtrate was stored under an argon atmosphere.

Preparation of Amine-Functionalized Composite Materials
The graphene oxide (GO) was prepared according to the literature-reported method [29]. GO (1 g) was dissolved in distilled water (50 mL) in a conical flask and sonicated for one hour. Then, cetyltrimethylammonium bromide (0.5 g), 2 M of NaOH (aq) (7 mL, 14 mmol), and H 2 O (480 g) were added to a conical flask and stirred for 30 min. The sonicated GO solution was slowly added to the mixture and stirred for 1 h. Then, tetraethyl orthosilicate (44.8 mmol) and 3-(2-aminoethylamino) propyl trimethoxysilane (AAPTMS) (1.68 mL) were added in sequence and stirred for 2 h at 70 • C. The products were isolated by a hot filtration, washed with water followed by ethanol, and dried in an oven. For the removal of the surfactant, we used an acid extraction technique. Then, the mixture dried at Nanomaterials 2021, 11, 2260 3 of 14 100 • C for overnight. The final sample was designated as AAPTMS@GO-MCM-41. The amine-functionalized zirconia and amine-functionalized mesoporous silica were prepared using the reported methods [30,31].

Preparation of Cu(0) Modified Composite Materials
The amine-functionalized graphene oxide-mesoporous silica composite material (1 g) was suspended in 50 mL water in a beaker. Then required amount of aqueous CuCl 2 .2H 2 O was added dropwise to achieve the 1, 5, and 10 wt% Cu materials. Then the solution was stirred for 30 min. Then, the plant extract reducing agent was added to the final mixture and stirred for another 4 h. Finally, the mixture was washed several times with double distilled water and hot water. Then, the product was dried in a vacuum oven at 100 • C for overnight. Hereafter the prepared samples are termed as xCu(0)-AAPTMS@RGO-MCM-41 (x = 1, 5 or 10 wt%).We also prepared amine-functionalized materials loaded with 5 wt% copper on mesoporous silica (5Cu(0)-AAPTMS@MCM-41), zirconia (5Cu(0)-AAPTMS@ZrO 2 ), and graphene oxide (5Cu(0)-AAPTMS@RGO). ICP-MS was used to calculate the exact percentage % of Cu present on the catalyst, which was found to be 0.91, 4.79, and 9.57.

Physico-Chemical Analytical Methods
The Bruker D8 Advance instrument was used for X-ray diffraction (XRD) study. The Jeol JEM-1010 electron microscope with iTEM software was used for the TEM study. Highresolution TEM images were recorded with Jeol JEM 2100 Electron Microscope. A JEOL JSM-6100 microscope was used for both SEM and EDX studies. The DeltaNu advantage 532™ Raman instrument was used for Raman spectra.

General Procedure for Catalytic Ullman C-C/C-O/C-N Coupling Reaction
The Ullman C-C coupling reaction was performed in a 50 mL round-bottomed flask. In the round-bottomed flask, the mixture of catalyst (0.03 g), water solvent (10 mL), Aryl halide (4.5 mmol), HCOONa (1.10 g), and KOH (1.40 g) was stirred for 5 h at 80 o C. Then, the products were extracted with diethyl ether. The final products were analyzed by an off-line Shimadzu gas chromatograph (GC-2010).
The Ullman C-N coupling reaction, Aryl halide (1 mmol), aniline (1.2 mmol), catalyst (0.03 g), and Cs 2 CO 3 (2.0 mmol) in DMF (1 mL) were stirred in a 50 mL flask for 6 h at 110 • C. Off-line GC-2010 was used to analyze the final. Figure 1 illustrates the X-ray diffraction spectra of (a)1 Cu(0)-AAPTMS@RGO-MCM-41, (b) 5Cu(0)-AAPTMS@RGO-MCM-41and (c) 10Cu(0)-AAPTMS@RGO-MCM-41 materials. In RGO, the main peak represents the (002) plane at a 2 θ value of 10.75 degrees [32]. During the preparation, we used both plant extract reducing agent and sonication to generate Cu nanoparticles. The (002) plane of the graphene oxide peak vanished as it formed reduced graphene oxide. In graphene oxide and MCM-41, no peaks were observed at a higher angle for mesoporous silica due to the amorphous nature of the silica material. Therefore, high angle XRD did not confirm the composite materials. For further confirmation, we used SEM and EDX studies. From this analysis, we confirmed the formation of reduced graphene oxide and mesoporous silica composite materials. In these XRD spectra, all the 1, 5, and 10 wt% samples gave three peaks at 2θ ≈ 43.47, 50.44, and 74.55 correspond to the (111), (200), and (220) planes of Cu metal nanoparticles, respectively [33]. Thus, the XRD pattern provides another confirmation about the Cu nanoparticle and reduced graphene oxide. tra, all the 1, 5, and 10 wt% samples gave three peaks at 2  43.47, 50.44, and 74.55 correspond to the (111), (200), and (220) planes of Cu metal nanoparticles, respectively. [33] Thus, the XRD pattern provides another confirmation about the Cu nanoparticle and reduced graphene oxide.  Figure 2. In these spectra, all the composite materials give the characteristic D and G bands. The bands at 1355 cm −1 represent the disorder in the sp 2 -hybridized carbon atoms, and 1604 cm −1 represents σ-sp 2 bonded C-atoms in carbon-based graphene materials. The D and G band position slightly shifted towards the higher wavenumber for all the samples. The shift was due to metal modification via molecular interaction. The Id/Ig ratios were 0.69, 0.73, and 0.72 for (a) 1Cu(0)-AAPTMS@RGO-MCM-41, (b) 5Cu(0)-AAPTMS@RGO-MCM-41, and (c) 10Cu(0)-AAPTMS@RGO-MCM-41 samples. The Id/Ig ratio of metal-modified functionalized composite materials increased the intensity of the Id/Ig ratio up to 0.1 compared with graphene oxide.  Figure 3 illustrates the Scanning electron microscopy images, transmission electron microscopy, and the SAAD pattern of the 5Cu(0)-AAPTMS@RGO-MCM-41 sample. The SEM images (Figure 3a,b) show that all the graphene oxide sheets converted to reduced graphene oxide, and some spherical particles represent the mesoporous silica. Thus, the carbon-based material and mesoporous silica formed the composite materials. The tiny particles on the surface of the composite material were due to the functionalization of composite material. The functional group increases the binding capacity of the metal particles. The spherical mesoporous silica particles and the Cu nanoparticles were confirmed from the TEM image of Figure 3c. The electron diffraction pattern gives information about the planes such as (111), (200), and (220), which resemble the d-spacing of the Cu phases as obtained from the powder X-ray diffraction study.   (Figure 3a-b) show that all the graphene oxide sheets converted to reduced graphene oxide, and some spherical particles represent the mesoporous silica. Thus, the carbon-based material and mesoporous silica formed the composite materials. The tiny particles on the surface of the composite material were due to the functionalization of composite material. The functional group increases the binding capacity of the metal particles. The spherical mesoporous silica particles and the Cu nanoparticles were confirmed from the TEM image of Figure 3c. The electron diffraction pattern gives information about the planes such as (111), (200), and (220), which resemble the d-spacing of the Cu phases as obtained from the powder X-ray diffraction study.   High-resolution images of (a) 5Cu(0)-AAPTMS@RGO-MCM-41 and (b) histogram of the particle size distribution for Cu nanoparticles are shown in Figure 4. In this image (Figure 4a), the big spherical particles are mesoaporous silica, represented with yellow lines. The reduced graphene oxide is also represented by yellow lines in Figure 4a. In this image, the red circles represent the Cu Nanoparticles. A histogram of the particle size distribution reflects the size of the particles. Figure 4b illustrates the particle size for Cu nanoparticles as 4-6.5 nm. High-resolution images of (a) 5Cu(0)-AAPTMS@RGO-MCM-41 and (b) histogram of the particle size distribution for Cu nanoparticles are shown in Figure 4. In this image (Figure 4a), the big spherical particles are mesoaporous silica, represented with yellow lines. The reduced graphene oxide is also represented by yellow lines in Figure 4a. In this image, the red circles represent the Cu Nanoparticles. A histogram of the particle size distribution reflects the size of the particles. Figure 4b illustrates the particle size for Cu nanoparticles as 4-6.5 nm. High-resolution images of (a) 5Cu(0)-AAPTMS@RGO-MCM-41 and (b) histogram of the particle size distribution for Cu nanoparticles are shown in Figure 4. In this image (Figure 4a), the big spherical particles are mesoaporous silica, represented with yellow lines. The reduced graphene oxide is also represented by yellow lines in Figure 4a. In this image, the red circles represent the Cu Nanoparticles. A histogram of the particle size distribution reflects the size of the particles. Figure 4b illustrates the particle size for Cu nanoparticles as 4-6.5 nm.

Catalyst Evaluation
In the present work, we studied the activity of Cu nanoparticles loaded on different functionalized supports as a catalyst for C-C, C-O, and C-N Ullmann coupling reactions. We initially investigated different wt% of Cu nanoparticles supported reduced graphene oxide-mesoporous silica material. Uniform distribution over the support surface was observed, only with 5 wt% material among the three Cu loadings. Hence, we prepared 5 wt% Cu on various supports and compared their activity.
The assessed the efficiency of water, DMF, THF, benzene, and toluene as solvents on the reaction and the effect of varying halo-substituents on benzene on the yields of the coupling reactions. In Ullmann C-C homo-coupling reaction, we used two iodobenzene molecules as the model substrate and potassium carbonate as a base with water as the solvent. The obtained yields with different catalysts summarized in Figure 6 illustrate that 5Cu(0)-AAPTMS@RGO-MCM-41 gave excellent yield (97%) of the biphenyl product as compared to other materials such as 5Cu(0)-AAPTMS@MCM-41 (87%), 5Cu(0)-AAPTMS@ZrO2 (84%), and 5Cu(0)-AAPTMS@GO (89%) under similar conditions. The superior yield may be due to the better distribution of Cu nanoparticles on RGO and MCM-41 composite surfaces. The 1Cu(0)-AAPTMS@RGO-MCM-41 gave a relatively lower yield (91%), which could be due to the fewer metal particles available on the catalyst surface. With 10Cu(0)-AAPTMS@RGO-MCM-41, the yield decreased from 97 to 93%. This decrease could be due to the increased loading of the metal agglomerate and offering less active sites of the surface of the composite material. Thus, 5Cu(0)-AAPTMS@RGO-MCM-41 material proved ideal for this coupling reaction. Li et al. [34] reported that MOF-253·0.05PdCl2catalyst gives 99% yield in DMSO/EtOH (20:1) at 120 °C for 10 h, while Pd/Ph-SBA-15 catalyst reportedly gave 75% yield at 100 °C for 10 h [35]. Wan et al. described that silica-carbon supported palladium catalyst offers 64% yield in water medium for 6 h [36]. Karim et al. [37] reported that Ausupported mesoporous silica gives 95% yield at 100 °C for 16 h. Varadwaj et al. Pd(0)

Catalyst Evaluation
In the present work, we studied the activity of Cu nanoparticles loaded on different functionalized supports as a catalyst for C-C, C-O, and C-N Ullmann coupling reactions. We initially investigated different wt% of Cu nanoparticles supported reduced graphene oxide-mesoporous silica material. Uniform distribution over the support surface was observed, only with 5 wt% material among the three Cu loadings. Hence, we prepared 5 wt% Cu on various supports and compared their activity.
The assessed the efficiency of water, DMF, THF, benzene, and toluene as solvents on the reaction and the effect of varying halo-substituents on benzene on the yields of the coupling reactions. In Ullmann C-C homo-coupling reaction, we used two iodobenzene molecules as the model substrate and potassium carbonate as a base with water as the solvent. The obtained yields with different catalysts summarized in Figure 6 illustrate that 5Cu(0)-AAPTMS@RGO-MCM-41 gave excellent yield (97%) of the biphenyl product as compared to other materials such as 5Cu (0) reported that Nanoparticles supported organo-functionalized clay gave 96% yield in a water medium at 80 °C for6 h [38]. The inherent disadvantages associated with these reports were higher temperature, longer reaction time and expensive metal catalysts. The current method giving 97% yield in 5 h at 80 °C in an aqueous medium offers superior yield, reaction time, solvent and temperature conditions.  Li et al. [34] reported that MOF-253·0.05PdCl 2 catalyst gives 99% yield in DMSO/EtOH (20:1) at 120 • C for 10 h, while Pd/Ph-SBA-15 catalyst reportedly gave 75% yield at 100 • C for 10 h [35]. Wan et al. described that silica-carbon supported palladium catalyst offers 64% yield in water medium for 6 h [36]. Karim et al. [37] reported that Au-supported mesoporous silica gives 95% yield at 100 • C for 16 h. Varadwaj et al. Pd(0) reported that Nanoparticles supported organo-functionalized clay gave 96% yield in a water medium at Nanomaterials 2021, 11, 2260 8 of 14 80 • C for6 h [38]. The inherent disadvantages associated with these reports were higher temperature, longer reaction time and expensive metal catalysts. The current method giving 97% yield in 5 h at 80 • C in an aqueous medium offers superior yield, reaction time, solvent and temperature conditions.
For investigating the Ullmann C-O coupling reaction, we used iodobenzene and phenol as the model reactants and potassium carbonate as base and DMF as the solvent. Figure 7 illustrates the obtained results. The 5Cu(0)-AAPTMS@RGO-MCM-41 gave the highest yield (94%) towards the C-O coupling reaction in a shorter time (7 h) at 100 • C temperature, while 1Cu(0)-AAPTMS@RGO-MCM-41 gave 87%, 10wt% gave 88% yields.   [42]. In most published methods, the yield towards C-O coupling was generally good, but reaction required high temperatures and long reaction times. We also prepared and assessed the activity of different Cu-loaded supported materials under comparable conditions. The examination of the table shows that our catalyst gave superior results at lower temperatures and shorter times than the other literature reported results.
The C-N coupling reaction between iodobenzene and aniline was investigated using potassium carbonate as a base and DMF as a solvent (Figure 8). 5Cu(0)-AAPTMS@RGO-MCM-41 gave superior yield (85%) towards C-N coupling reaction compared to graphene oxide (76%), zirconia (69%), and mesoporous silica (74%) supported materials. The 1% and 10Cu (0)-AAPTMS@RGO-MCM-41 composites offered 80% and 83% yields, respectively. Literature review shows that only very few articles on C-N coupling reactions. Pan et al. [43] reported that Cu nanoparticles-modified silicon nanowires give 89% yield in the presence of DMSO, at 110 °C for 18 h.   [42]. In most published methods, the yield towards C-O coupling was generally good, but reaction required high temperatures and long reaction times. We also prepared and assessed the activity of different Cu-loaded supported materials under comparable conditions. The examination of the table shows that our catalyst gave superior results at lower temperatures and shorter times than the other literature reported results.
The C-N coupling reaction between iodobenzene and aniline was investigated using potassium carbonate as a base and DMF as a solvent (Figure 8). 5Cu(0)-AAPTMS@RGO-MCM-41 gave superior yield (85%) towards C-N coupling reaction compared to graphene oxide (76%), zirconia (69%), and mesoporous silica (74%) supported materials. The 1% and 10Cu (0)-AAPTMS@RGO-MCM-41 composites offered 80% and 83% yields, respectively. Literature review shows that only very few articles on C-N coupling reactions. Pan et al. [43] reported that Cu nanoparticles-modified silicon nanowires give 89% yield in the presence of DMSO, at 110 • C for 18 h. In both homo and hetero coupling reactions, the solvent plays a crucial role in the selectivity and yield of the reaction product. Therefore, we investigated the effect of different media (solvent) on the three Ullmann coupling reactions, and the obtained results are summarized in Tables 1-3. Toluene and benzene gave meagre yield towards C-C, C-O and C-N coupling products, while polar solvents THF and DMF gave excellent returns. As water is a green and cost-effective solvent, it is the preferred solvent. Some researchers explored water as a co-solvent for Ulmann C-C homo-coupling reaction. We examined the efficiency of the Cu nanoparticle-doped organo-functionalized composite material as a catalyst for C-C homo-coupling with water as a solvent, and fascinatingly excellent yield was obtained (Table 1, entry 5). Similar to the C-C coupling reaction, nonpolar solvent gave lower products for C-O and C-N coupling reactions, and polar solvents offered good yields (Tables 2 and 3). Generally, polar solvents increase the rate of trans-metalation but decrease the stability of the catalyst. A Cu catalyst is capable of facilitating faster transmetalation in a polar medium. As anticipated, 5Cu(0)-AAPTMS@RGO-MCM-41 material increased the yield of the coupling product in a polar solvent while maintaining the stability of the catalyst. Table 1. The effect of different solvents on the yield for the C-C Ullmann coupling reaction using 5 Cu(0)-AAPTMS@RGO-MCM-41 as a catalyst a . 1  Toluene  79  2  Benzene  68  3  DMF  99  4  THF  98  5 Water 97 In both homo and hetero coupling reactions, the solvent plays a crucial role in the selectivity and yield of the reaction product. Therefore, we investigated the effect of different media (solvent) on the three Ullmann coupling reactions, and the obtained results are summarized in Tables 1-3. Toluene and benzene gave meagre yield towards C-C, C-O and C-N coupling products, while polar solvents THF and DMF gave excellent returns. As water is a green and cost-effective solvent, it is the preferred solvent. Some researchers explored water as a co-solvent for Ulmann C-C homo-coupling reaction. We examined the efficiency of the Cu nanoparticle-doped organo-functionalized composite material as a catalyst for C-C homo-coupling with water as a solvent, and fascinatingly excellent yield was obtained (Table 1, entry 5). Similar to the C-C coupling reaction, nonpolar solvent gave lower products for C-O and C-N coupling reactions, and polar solvents offered good yields (Tables 2 and 3). Generally, polar solvents increase the rate of trans-metalation but decrease the stability of the catalyst. A Cu catalyst is capable of facilitating faster trans-metalation in a polar medium. As anticipated, 5Cu(0)-AAPTMS@RGO-MCM-41 material increased the yield of the coupling product in a polar solvent while maintaining the stability of the catalyst.

Yield (%) C-C Coupling Product
The yields for reactions of bromobenzene and chlorobenzene with phenol and aniline are summarized in Table 4. The 5Cu(0)-AAPTMS@RGO-MCM-41 catalyst performed well for all three reaction types except for lower yields with Cl-substituents for C-O and C-N coupling reactions. Bromobenzene offered good to excellent yields in all three coupling reactions. It also gave good gains with Cl-substituted benzene for the C-C coupling reaction. The C-Br, C-Cl, and C-I bond energies are 281.4, 340.2, and 222.6 kJ mol −1 . According to MOT theory, the C-I bond easily breaks due to low energy and forms C-C, C-O, and C-N products compared to C-Br and C-Cl bond. Table 1. The effect of different solvents on the yield for the C-C Ullmann coupling reaction using 5 Cu(0)-AAPTMS@RGO-MCM-41 as a catalyst a .

Yield (%) C-C Coupling Product
was obtained (Table 1, entry 5). Similar to the C-C coupling reaction, nonpolar solvent gave lower products for C-O and C-N coupling reactions, and polar solvents offered good yields (Tables 2 and 3). Generally, polar solvents increase the rate of trans-metalation but decrease the stability of the catalyst. A Cu catalyst is capable of facilitating faster transmetalation in a polar medium. As anticipated, 5Cu(0)-AAPTMS@RGO-MCM-41 material increased the yield of the coupling product in a polar solvent while maintaining the stability of the catalyst.    The yields for reactions of bromobenzene and chlorobenzene with phenol and aniline are summarized in Table 4. The 5Cu(0)-AAPTMS@RGO-MCM-41 catalyst performed well for all three reaction types except for lower yields with Cl-substituents for C-O and C-N coupling reactions. Bromobenzene offered good to excellent yields in all three coupling reactions. It also gave good gains with Cl-substituted benzene for the C-C coupling reaction. The C-Br, C-Cl, and C-I bond energies are 281.4, 340.2, and 222.6 kJ mol −1 . According to MOT theory, the C-I bond easily breaks due to low energy and forms C-C, C-O, and C-N products compared to C-Br and C-Cl bond.    O   1  Toluene  63  2  Benzene  49  3  DMF  94  4  THF  90  5 Water 89 a Reaction conditions: Temperature, 100 °C; time, 7 h; catalyst, 0.03 g; solvent, 1 mL. Reactants: Aryl halides (1.5 mmol); Phenol (1.0 mmol); CsCO3 (2 mmol). The yields for reactions of bromobenzene and chlorobenzene with phenol and aniline are summarized in Table 4. The 5Cu(0)-AAPTMS@RGO-MCM-41 catalyst performed well for all three reaction types except for lower yields with Cl-substituents for C-O and C-N coupling reactions. Bromobenzene offered good to excellent yields in all three coupling reactions. It also gave good gains with Cl-substituted benzene for the C-C coupling reaction. The C-Br, C-Cl, and C-I bond energies are 281.4, 340.2, and 222.6 kJ mol −1 . According to MOT theory, the C-I bond easily breaks due to low energy and forms C-C, C-O, and C-N products compared to C-Br and C-Cl bond.  Figure 9 shows a yield versus time plot, which illustrates the significance of the catalyst towards the Ullman C-C coupling reaction. The red line connecting with yellow squares indicates the yield of biphenyl in the presence of a catalyst. During the experiment, after 2.5 h of the reaction, the catalyst was removed by filtration. The reaction was monitored for another 2.5 h in the absence of the catalyst. The yield of the biphenyl product did not increase during that period, suggesting that Cu from the composite did not leach to the reaction medium. These results are indicated by a blue line connected to the red cube in Figure 9. Hence, the Cu metal particles were tightly bonded and stable with functionalized composite material. Table 4. Yields for C-C, C-O, and C-N coupling reactions with different substrates with 5 Cu(0)-AAPTMS@RGO-MCM-41 as a catalyst.
The yields for reactions of bromobenzene and chlorobenzene with phenol and aniline are summarized in Table 4. The 5Cu(0)-AAPTMS@RGO-MCM-41 catalyst performed well for all three reaction types except for lower yields with Cl-substituents for C-O and C-N coupling reactions. Bromobenzene offered good to excellent yields in all three coupling reactions. It also gave good gains with Cl-substituted benzene for the C-C coupling reaction. The C-Br, C-Cl, and C-I bond energies are 281.4, 340.2, and 222.6 kJ mol −1 . According to MOT theory, the C-I bond easily breaks due to low energy and forms C-C, C-O, and C-N products compared to C-Br and C-Cl bond. Table 4. Yields for C-C, C-O, and C-N coupling reactions with different substrates with 5 Cu(0)-AAPTMS@RGO-MCM-41 as a catalyst. The yields for reactions of bromobenzene and chlorobenzene with phenol and aniline are summarized in Table 4. The 5Cu(0)-AAPTMS@RGO-MCM-41 catalyst performed well for all three reaction types except for lower yields with Cl-substituents for C-O and C-N coupling reactions. Bromobenzene offered good to excellent yields in all three coupling reactions. It also gave good gains with Cl-substituted benzene for the C-C coupling reaction. The C-Br, C-Cl, and C-I bond energies are 281.4, 340.2, and 222.6 kJ mol −1 . According to MOT theory, the C-I bond easily breaks due to low energy and forms C-C, C-O, and C-N products compared to C-Br and C-Cl bond. The yields for reactions of bromobenzene and chlorobenzene with phenol and aniline are summarized in Table 4. The 5Cu(0)-AAPTMS@RGO-MCM-41 catalyst performed well for all three reaction types except for lower yields with Cl-substituents for C-O and C-N coupling reactions. Bromobenzene offered good to excellent yields in all three coupling reactions. It also gave good gains with Cl-substituted benzene for the C-C coupling reaction. The C-Br, C-Cl, and C-I bond energies are 281.4, 340.2, and 222.6 kJ mol −1 . According to MOT theory, the C-I bond easily breaks due to low energy and forms C-C, C-O, and C-N products compared to C-Br and C-Cl bond. Table 4. Yields for C-C, C-O, and C-N coupling reactions with different substrates with 5 Cu(0)-AAPTMS@RGO-MCM-41 as a catalyst. The yields for reactions of bromobenzene and chlorobenzene with phenol and aniline are summarized in Table 4. The 5Cu(0)-AAPTMS@RGO-MCM-41 catalyst performed well for all three reaction types except for lower yields with Cl-substituents for C-O and C-N coupling reactions. Bromobenzene offered good to excellent yields in all three coupling reactions. It also gave good gains with Cl-substituted benzene for the C-C coupling reaction. The C-Br, C-Cl, and C-I bond energies are 281.4, 340.2, and 222.6 kJ mol −1 . According to MOT theory, the C-I bond easily breaks due to low energy and forms C-C, C-O, and C-N products compared to C-Br and C-Cl bond. Table 4. Yields for C-C, C-O, and C-N coupling reactions with different substrates with 5 Cu(0)-AAPTMS@RGO-MCM-41 as a catalyst. The yields for reactions of bromobenzene and chlorobenzene with phenol and aniline are summarized in Table 4. The 5Cu(0)-AAPTMS@RGO-MCM-41 catalyst performed well for all three reaction types except for lower yields with Cl-substituents for C-O and C-N coupling reactions. Bromobenzene offered good to excellent yields in all three coupling reactions. It also gave good gains with Cl-substituted benzene for the C-C coupling reaction. The C-Br, C-Cl, and C-I bond energies are 281.4, 340.2, and 222.6 kJ mol −1 . According to MOT theory, the C-I bond easily breaks due to low energy and forms C-C, C-O, and C-N products compared to C-Br and C-Cl bond.  Figure 9 shows a yield versus time plot, which illustrates the significance of the catalyst towards the Ullman C-C coupling reaction. The red line connecting with yellow squares indicates the yield of biphenyl in the presence of a catalyst. During the experiment, after 2.5 h of the reaction, the catalyst was removed by filtration. The reaction was monitored for another 2.5 h in the absence of the catalyst. The yield of the biphenyl product did not increase during that period, suggesting that Cu from the composite did not leach to the reaction medium. These results are indicated by a blue line connected to the red cube in Figure 9. Hence, the Cu metal particles were tightly bonded and stable with functionalized composite material.   Figure 9 shows a yield versus time plot, which illustrates the significance of the catalyst towards the Ullman C-C coupling reaction. The red line connecting with yellow squares indicates the yield of biphenyl in the presence of a catalyst. During the experiment, after 2.5 h of the reaction, the catalyst was removed by filtration. The reaction was monitored for another 2.5 h in the absence of the catalyst. The yield of the biphenyl product did not increase during that period, suggesting that Cu from the composite did not leach to the reaction medium. These results are indicated by a blue line connected to the red cube in Figure 9. Hence, the Cu metal particles were tightly bonded and stable with functionalized composite material. In heterogeneous catalysis, the material's recyclability is paramount, and it is contingent primarily on the stability of the catalyst. The activity of catalyst materials can decline due to the leaching effect of the active metal or the agglomeration of the metal particles. For robustness, the recovered catalyst was reused after regeneration by calcination. Up to the fourth cycle, the yield of the product has not changed. The active metal particle did In heterogeneous catalysis, the material's recyclability is paramount, and it is contingent primarily on the stability of the catalyst. The activity of catalyst materials can decline due to the leaching effect of the active metal or the agglomeration of the metal particles. For robustness, the recovered catalyst was reused after regeneration by calcination. Up to the fourth cycle, the yield of the product has not changed. The active metal particle did not leach out in the reaction medium because of the strong bonding between metal nanoparticles and functionalized composite material. On the fifth cycle to onwards, some reduction in its productivity was observed in Figure 10. not leach out in the reaction medium because of the strong bonding between metal nanoparticles and functionalized composite material. On the fifth cycle to onwards, some reduction in its productivity was observed in Figure 10.

Conclusions
In conclusion, we demonstrate the synthesis of amine-functionalized composites with well-dispersed Cu particles (4-6.5 nm) using a green reducing agent, a plant extract. 5Cu(0)-AAPTMS@RGO-MCM-41 displayed excellent catalytic activity towards all the C-C, C-O, and C-N coupling reactions with different substrates and showed recyclability up to the fourth cycle. The strong bonding between the metal nanoparticle and functional groups of functionalized composite material prevents the aggregation of metal particles and leaching during the reaction time. XRD and TEM analysis confirmed the size of Cu nanoparticles.
Future perspectives of the proposed method: (i) Leaf extract (Wallich Spurge) as a green and eco-friendly reducing agent, (ii) the functionalization reduced graphene oxide and silica composites preventing nanoparticle agglomeration and (iii) the novel nanocomposite possess potential applications as a catalyst in different C-C and C-hetero atom coupling reactions.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author