Novel Synthesis and Characterization of Nano-Activated Carbon Derived from Agricultural Orange Peel Waste

In general, material characterization needs to be appropriate for its intended use, meaning that the method selected for characterization ought to consider the type of data needed for the specific application of the material being examined.

As was previously indicated, the ultimate product and the source of the activated carbon should both be taken into consideration when characterizing material obtained from lignocellulosic sources. Analyzing the raw material to ascertain its purity, primary chemical structure, particle shape, and size. Important details regarding the characteristics of the finished product can be found in the proximate analysis carried out before the carbonization phase and the ultimate analysis carried out afterward [11-14].

The sample's morphology was examined using a transmission electron microscope (TEM) equipped with a Philips model CM120 and a scanning electron microscope (SEM) equipped with a Jasco 4200 Japan instrument for FTIR testing. Measurements using energy dispersive spectroscopy (EDS) were done at Oxford Instruments, UK. Using a Raman thermos nickel Raman spectrometer from the USA, Raman spectroscopy was performed. Powders were subjected to analysis in an X-ray diffraction apparatus with a Siemens model D500 detector. Test (BET) for Braunare and Eimattauer conducted by Quanta Chrome NOVA 2200E in Germany.

3.1 XRD test

The X-ray diffraction of OP and AC was used to evaluate the crystalline form. A crystalline is composed of regularly arranged in a 3D zone. In contrast, amorphous materials have an unregular arrangement and atoms are randomly distributed in the 3D zone [15]. The best calcination temperature is 250℃; it was checked with crystal phase, weight loss and surface area [16]. running with CuKα radiation at 45 kV and 25 mA. At a scan speed of 0.42° s^-1, within the 2ϑ range, which extends from 10° to 90°, XRD patterns were obtained. The diffractograms displayed in Figure 2 lack a sharp peak and have broad peaks instead. The powdered orange peel's amorphous nature can be indicated by the lack of a distinct peak. In contrast, a large peak in Figure 3 (between 2ϑ= from (28.4822 to 29.0547) indicated the beginnings of a crystalline carbonaceous structure, which improved layer alignment [17].

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Figure 2. XRD test of raw powder orange peel

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Figure 3. XRD test of activated carbon of orange peel

The crystal structure of the produced activated carbon was analyzed using an X-ray diffractometer. The diffraction patterns of carbon derived from orange peel are indicated by the following planes: (002) at 13.4°, (101) at 19.5°, (111) at 29.4°, (020) at 34.1°, and (022) at 39.4°, as illustrated in Figure 3 [18]. Additionally, there are extra peaks present, which may be attributed to the presence of pure biomass and the graphitic structure of carbon [12 ,13, 19, 20].

XRD measurements described the structures of the synthesized OP and OP-AC samples, the results of which are displayed in Figure 2 and Figure 3. The OP samples show a wide Peake, which refers to poor crystallization, as confirmed by the XRD findings. The two large peaks at 24.24° and 43.01° are attributed to the reflection from the carbon's (002) and (101) planes. The massive peaks at 24.24 result from the amorphous nature of the carbon molecules and diffusion scattering of the degree of graphitization [21].

It was observed that in OP-AC, the (002) peak's intensity is noticeably lower, but its widening is higher. It indicates that the samples have a high density of pores. Furthermore, the interlayer spacing is calculated using Bragg's equation, which states that 2d sinϑ = nλ. For the FG sample, the crystallite size is 25.84 nm, as calculated below. The observed d spacing of the AC-OP is larger than the OP graphite results [22].

3.1.1 Crystallite size

The crystallite size and average crystallite size were calculated from XRD data. The crystallite size, D, was calculated using Scherrer’s equation, and the results are presented in Table 1.

$D=\frac{K \lambda}{\beta_{h k l} \cos \vartheta_{h k l}}$             (1)

where,

D = size in (nm)

Κ = 0.95-0.98 (shape factor)

Λ = 0.154 nm (X-ray wavelength)

$\beta_{h k l}$  = half-width of the diffraction band (FWHM) (radians)

$\vartheta_{h k l}$ = Bragg diffraction angle (peak position in radians

Table 1. Value of the above equation obtained by using origin lab soft

Average size= 25.84 nm.

3.2 SEM test characterization

Observed the morphology powder of orange peel and activated carbon from orange peel by using scanning electron microscope (SEM). The SEM images at Figure 4(a, b and c) for orange peel show at scale of (a) 2µ and (b) 5µm and (c) 500nm an irregular surface morphology. The surface of activated carbon materials in Figure 5(a, b, and c), shown at scales of 2 µm, 10 µm, and 500 nm, is characterized by a well-developed structure, as evidenced by the presence of holes with various diameters and shapes, including irregularly shaped holes. The existence of a porous structure facilitates the diffusion process indispensable in heterogeneous catalysis for the transport of both reactants and products [23]. This coarse texture comprises varying-sized pores, making it useful for adsorption purposes [24].

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(a) 2 µm

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(b) 5 µm

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(c) 500 nm

Figure 4. SEM test of powder orange peel (a) at a scale of 2µ, (b) at a scale of 5µ, and (c) at a 500nm scale

The porous channel in the OP structures was visible in the scanning electron microscope (SEM) micrographs shown in Figure 5, resulting from the pyrolysis and chemical activation of carbon produced from the orange peel precursor. The pre-carbonized precursor was pyrolyzed without a chemical activation agent to create a structure with asymmetric morphologies, as shown in Figure 5(b). Studies [25, 26] show carbon develops in a porous condition when a channel assembly is visible. This gives electrolyte ions access a greater surface area and a transfer pathway along the charge storage progression.

SEM imaging reveals the surface morphology and pore distribution of a material. A high surface area, often associated with a porous structure, is critical for enhancing adsorption capacity. Greater surface area provides more active sites for adsorption, enabling the material to capture larger amounts of adsorbates.

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(a) 2 µm

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(b) 5 µm

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(c) 500 nm

Figure 5. SEM test of activated carbon a) at the scale of 2µ, (b) at the scale of 5µ, and (c) at a 500nm scale

3.3 Energy dispersive spectroscopy (EDS) test characteristic

Using energy dispersive spectroscopy (EDS) to find the orange peel sample's and activated carbon's chemical composition. The test reports are displayed in Figure 6(a), 10µm electron schema of the orange peel particle. A diagram of the particle content of orange peel is shown in Figure 6(b) and Table 2. These diagrams and table show that the OP is constituted of some elements, such as, carbon (C), Oxygen (O), potassium (K) and calcium (Ca).

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(a) 10 µm electron image of the orange peel particle

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(b) A diagram of the particle content of orange peel of oxygenated groups on its surface

Figure 6. EDS test of orange peel

While for activated carbon, Figure 7 shows the following results: (a) a 10 µm electron image of the activated carbon, (b) a schema of the particle content of activated carbon are carbon (C), Oxygen (O), potassium (K), calcium (Ca), Magnesium (Mg), phosphorus (P), surfer (S), and chlorine (Cl). The majority of these components are said to be a feature of the makeup of orange peels by studies [27, 28]. Table 3 shows that the concentrations of K (8.65%) and Ca (6.87%) are significantly greater than those of the other elements, yet they are nevertheless regarded as typical for Iraqi oranges. Oxygen's presence indicates that the activated carbon has a high content of oxygen-containing functional groups.

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(a) 10 µm electron image of the activated carbon

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(b) A diagram of the particle content of activated carbon

Figure 7. EDS test of activated carbon

Table 2. EDS test of the particle content of orange peel

Table 3. EDS test of the particle content of the particle content of activated carbon from orange peel

3.4 FTIR test

There is a clear structural similarity when comparing the wavelength of the orange peel (OP) from the graph in Figure 8 with the data in Table 4. The bands of the hydroxyl groups of proteins and carbohydrates are visible at 3422.06 cm^-1, while the C-H stretching vibrations of aliphatic groups are observed at 2919.7 cm⁻¹. At 2346.94 cm^-1, certain weak bands are linked to C=C conjugated and C=C bonds, depending on the vegetable origin of the samples. The bands at 1750 cm^-1 correspond to the C=O group, and a strong peak appears at 1637.27 cm⁻¹, corresponding to the C=O amide I group. At 1457.92 cm⁻¹, stretching -C=O, inorganic carbonate is found at the peak. the protein structures' amide III band at (1327.75 cm^-1), as well as the C–X of fluoride at (1057.76 cm^-1) and chloride at (669.178 cm^-1).

Figure 9 depicts the AC absorption spectrum. The stretching of the O-H group is connected to the peaks at (3427.78 cm^-1). On the other hand, the (2917.94 cm^-1) peak is caused by the C-H stretching [29]. The additional peaks at (2345.94 cm^-1) and (1627.22 cm^-1) are connected to C=C functional groups (1457.28 cm^-1) are connected to C=O functional groups. The peak at (1057.16 cm^-1) is attributed to the C-O deformation of the aromatic group of graphitic units. These peaks demonstrate the presence of hydrophilic functional groups on the activated carbon's surface [30].

The presence or absence of functional groups in the OP and AC-OP samples was determined using FTIR spectroscopy; the results are displayed in Figures 8 and 9. The majority of the functional groups are present in the FTIR spectra of OP and AC-OP. In contrast to OP, AC-OP exhibits lower-intensity absorbance peaks following the activation process. As a result, the various functional groups present in OP and AC-OP may give rise to pores.

Table 4. List of band assignments for FTIR

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Figure 8. Test of powder orange peel

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Figure 9. FTIR test of activated carbon from orange peel

3.5 TEM studies

TEM measurements were used to analyze the synthetic materials' structural morphologies. Figure 10 displays the OP powder's TEM image pattern results. Figure 11 depicts the porous and densely linked frameworks with the crystallinity of AC-OP. This kind of AC-OP texture morphology suggests that the pores that are created during the carbonization and activation process help with ion diffusion within the carbon texture [31].

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(a) 60 nm

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(b) 200 nm

Figure 10. TEM test of orange peel (a) at scale of 200 nm and (b) at scale of 60 nm

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(a) 60 nm

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(b) 200 nm

Figure 11. TEM test of activated carbon orange peel (a) at a scale of 200 nm and (b) at a scale of 60 nm

3.6 Raman spectrum

High-quality graphene can be quickly identified by Raman spectroscopy. Figure 12 and Figure 13 show the Raman spectroscopy graph of orange peel (OP) and activated carbon sourced from orange peel (OP-AC) respectively, these diagrams show a multi narrow peaks the high centered at (415.21 and 317.39) cm^-1 for OP and (1533.23 and 1580.7) cm^-1 for OP-AC. These peaks are ascribed to the intensity of the 2D band relative to the G band (I_2D/I_G) =2908.29/1589.74=1.829 greater than > 0.5 which means a purity measure. Additionally, Theis peaks at ~2914.98 cm^-1 and ~3045.24 cm⁻¹, respectively, emphasize the turbostratic nature of FG.

Figure 12. Raman spectroscopy test of powder orange peel

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Figure 13. Raman spectroscopy test of activated Carbone from orange peel

3.7 BET analysis

The physicochemical properties of the AC and OP surfaces, including total pore volume, mean pore diameter, and specific surface area, were determined using BET surface area analysis. The pore structure properties are presented in Table 5. The BET test refers to the Brunauer–Emmett–Teller (BET) analysis, which is a widely used method for determining the specific surface area of a material. This test is based on the adsorption of gas molecules (commonly nitrogen, N₂) onto the surface of a material at a constant temperature (typically 77 K, the boiling point of liquid nitrogen). The specific surface areas (SBET) of AC and OP were calculated using the BET method [30], yielding values of 7.9168 m²/g and 3.879 m²/g, respectively. The BJH method [23] was applied to analyze the pore size and volume.

The total pore volumes of AC and OP were determined to be 0.027785 cm³/g and 0.01789 cm³/g, respectively, at P/P₀ = 0.99 from N₂ single-point adsorption. The mean pore widths of AC and OP were 14.039 nm and 18.448 nm, respectively. These values indicate the mesoporous nature of the materials, as porous materials are classified as microporous (less than 2 nm), mesoporous (between 2 and 50 nm), or microporous (greater than 50 nm) [32, 33]. The surface area and pore volume of macropores, mesopores, and micropores can be determined using BJH, the t-plot approach, and BET [34].

In adsorption applications, the BET surface area and pore size distribution are fundamental parameters that determine the efficiency and capacity of the adsorbent. A higher BET surface area provides more adsorption sites, while an appropriate pore size distribution ensures that adsorbates can efficiently access these sites. This leads to better performance in various applications such as gas storage, water treatment, and catalysis. Understanding and optimizing both properties is essential for designing advanced materials tailored to specific adsorption processes.

Surface area is crucial in determining the active sites available for contaminant adsorption. Increasing the surface area of a material enhances its ability to adsorb a larger quantity of pollutants [35]. The N₂ adsorption-desorption isotherms were used to measure the specific surface area and porous structure of the prepared activated carbon. Techniques such as BET and BJH were employed to calculate the surface area of the prepared activated carbon [36]. The surface area (BET) and porosity are key indicators of optimal preparation conditions. As shown in Figure 9, the volume adsorbed increases with increasing relative pressure. The SBET and total pore volume (VT) of the prepared activated carbon are influenced by the type of agricultural waste used. The carbonization and activation processes improved the adsorption capacity and efficiency by increasing the surface area of the adsorbent. For comparison, the physical properties of tea waste before and after activation show that the surface area increased from 0.735 m²/g (before activation) to 72.857 m²/g (after activation), similar increased in the surface area as the results obtained in study [37].