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Article

Decoration of Reduced Graphene Oxide with Magnesium Oxide during Reflux Reaction and Assessment of Its Antioxidant Properties

by
Aicha Bensouici
1,*,
Nacera Baali
2,*,
Roumaissa Bouloudenine
1 and
Giorgio Speranza
3
1
Laboratory of Mathematical and Subatomic Physics, Department of Physics, Mentouri Brothers University, Constantine 25000, Algeria
2
Department of Animal Biology, Mentouri Brothers University, Constantine 25000, Algeria
3
Fondazione Bruno Kessler, 38123 Trento, Italy
*
Authors to whom correspondence should be addressed.
C 2022, 8(4), 49; https://doi.org/10.3390/c8040049
Submission received: 20 August 2022 / Revised: 25 September 2022 / Accepted: 26 September 2022 / Published: 30 September 2022
(This article belongs to the Special Issue Carbon-Based Catalyst (2nd Edition))
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Abstract

:
The aim of this work is the reduction and decoration of graphene oxide (GO) with magnesium oxide (MgO). In this work, GO was synthesized using modified Hummers’ protocol with (1:2), (1:3) and (1:4) graphite:potassium permanganate mass ratios. Subsequently, all GO samples (GO1:2, GO1:3, GO1:4) were reduced and decorated with magnesium oxide nanoparticles using a reflux technique at 100 °C for 2 h. Sample characterization using X-ray diffraction (XRD) reveals the presence of peaks relative to two different magnesium (Mg) phases: magnesium oxide (MgO) and magnesium hydroxide (Mg(OH)2). The presence of these spectral features, although characterized by a remarkable broadening, confirms the successful synthesis of Mg(OH)2-rGO-MgO nanocomposites. X-ray photoelectron spectroscopy (XPS) spectra indicate the presence of peaks assigned to C, O and Mg. The analysis of the high-resolution XPS spectra of these elements confirms once again the presence of Mg(OH)2-rGO-MgO compounds. The low temperature synthesis of Mg(OH)2-rGO-MgO nanocomposite exhibiting superior catalytic properties compared to MgO–rGO nanoparticles is an important step forward with respect to the current state of the art. The antioxidant activity of six nanocomposites, namely GO1:2, GO1:3, GO1:4, MgO–rGO1:2, MgO–rGO1:3 and MgO–rGO1:4, was determined using standard protocols based on a DPPH radicals scavenging assay, an H2O2 scavenging assay, and a phosphomolybdate assay. All our samples exhibited dose-dependent antioxidant activity. Interestingly, among the different synthesized nanoparticles, GO1:4 and MgO–rGO1:4 showed the best performances.

1. Introduction

Throughout the last few decades, carbon nanoparticles have attracted growing attention. Extensive efforts were made to elaborate innovative nanocomposites possessing superior physical and chemical properties for biomedicine. The functionalization of carbon allotropes with different chemical elements and/or metal oxides paves the way to new advanced applications. By isolating graphene for the first time, Nobel Prize winners K.S. Novoselov and A.K. Geim (2004) pioneered a new era of materials science and condensed-matter physics. The unique physical and chemical properties of graphene have attracted the attention of the researchers of this material and its derivatives. Graphene is an atom-thick sheet of hexagonally sp2-bonded carbon atoms. It is highly flexible, but C–C bonds are harder than those of diamond, leading to a tensile strength of 130 GPa and Young’s Modulus of 1 TPa [1]. Graphene is considered a zero-gap semiconductor, and the sp2 hybridization combined with the quantum confinement along the z-direction results in very high electronic mobility [2] and high thermal conductivity [3]. Low-cost large-scale graphene production is realized through the oxidation of graphite powder in sulfuric acid solution using modified Hummers’ synthesis protocol, resulting in a pasty powder of graphene oxide (GO) [4]. Then, reduced graphene oxide (rGO) can be obtained from GO through electrochemical, chemical or thermal reduction [5]. GO and rGO possess interesting properties regarding the reduction of reactive oxygen species (ROS). The mechanism at the basis of this property was elucidated in the work by Y. Qui et al. [6]. Since this ROS scavenging property may have important applications in biomedicine it was studied in living cells. In the work by S.C Reshma et al. [7], authors studied the nano–biointeractions of rGO and pegylated rGO with lung alveolar epithelial A549 cells. Results show that rGO elicited oxidative stress and mediated apoptosis in the cells by inducing ROS. Conversely, rGO was found to scavenge ROS efficiently. To improve the ROS scavenging properties of rGO, decoration with metal oxide can be performed. This result is confirmed in the study by D. Suresh et al. [8], which emphasizes an improved scavenging activity of rGO.
In addition to graphene oxide and/or reduced graphene oxide intrinsic properties, a number of nanocomposites may be attached to the graphene surface with an appropriate functionalization. The latter allows the grafting of desired molecules or nanoparticles, thus driving the interaction with the environment. Among other things, functionalization with metals and metal oxides, graphene and its derivatives present very interesting electrochemical and biomedical properties [9]. With respect to Mg, according to Seham K. Abdel Aal et al., hybrid nanocomposites MgO–rGO/Fe2O3–rGO showed magnetic properties and a high thermal stability over a wide range of temperatures [10]. This new material can be utilized in various different fields, such as composites, energy, electronics, water splitting and biomedicine [11,12,13].
Concerning metal/metal oxide decorated graphene, the current developments for energy storage application was recently reviewed in [14]. The current literature shows that in electrochemical capacitors, the synergistic properties of metal/metal oxide decorated graphene result in a substantial improvement in rate capability, capacity and cycling stability with respect to their individual components. The role of metal oxide nanomaterials has been studied with excellent results in biomedicine. Metal oxide nanoparticles, such as Ag2O, FeO, MnO2, CuO, Bi2O3, ZnO, MgO, TiO2, CaO, Al2O3, etc., have been known to show potential antioxidant and antibacterial activity [15]. It is worth noting that biological activities, including the antioxidant activities of nanoparticles, are also affected by the synthesis methods, the structure of the obtained samples and reducing and stabilizing agents [16]. In our previous research, we explored the synthesis of GO using a modified Hummers’ method at different graphite: KMnO4 ratios (1:2, 1:3 and 1:4 ratios). Then the GO produced using the different molar ratios was successfully decorated with ZnO, leading to a ZnO–rGO nanocomposite. The antioxidant properties ofZnO–rGO was then studied and the ZnO–rGO (1:4) nanocomposites showed the best performances [17].
These results encouraged us to go forward in our research and use the same GO1:2, GO1:3 and GO1:4 as host matrices to support magnesium-oxide-based nanoparticles. Several theoretical studies using DFT or first principle calculations confirm the stability and strong cohesion of a MgO–rGO nanocomposite. J. Ryou et al. performed DFT calculations of carbon atom adsorption on an MgO (100) surface [18]. Carbon atoms show the most stable behavior on top oxygen sites of MgO surfaces. By increasing the number of carbon atoms, it forms a chain-like or graphene-like structure on the MgO surface [18]. This effective synergy between MgO and graphene atoms can explain the successful synthesis of the MgO–rGO nanocomposite obtained in our experiments. Furthermore, first principle calculations using the Vienna Ab Initio Simulation package (VASP) with projector augmented wave method (PAW) pseudopotentials were carried out by L. Liu et al. to understand the interaction between the interface between (Mg, MgO, Mg(OH)2) and (GO, rGO) [19]. Interestingly, a strong cohesion was found for the MgO–rGO interface compared to the weak cohesion in Mg(OH)2–rGO [19]. In the work by H. Xu at al., the DFT calculation confirms lower MgO reactivity towards H2S, corresponding to strong corrosion resistance. Hence, the MgO–rGO compound exhibits excellent catalytic activity that is higher than that of its counterparts [20].
There are very few works in the literature exploring the ROS scavenging properties of metal oxide decorated surface of rGO. The aim of the present work is to study the ROS scavenging properties of MgO–rGO nanocomposites never investigated before. The investigation of the structural and chemical properties was analyzed using XRD and XPS, while their antioxidant properties were assessed using a DPPH scavenging assay, H2O2 scavenging assay, and a phosphomolybdate assay (TAC: total antioxidant activity).
Contrary to monolayer graphene, showing good thermal stability at temperatures lower than 500 °C (<600 °C temperatures for bilayer graphene) [21], it is well known that GO exhibits lower thermal stability due to the presence of oxygen functional groups with defective basal plane structures (carboxyl and lactol groups) [22,23]. According to C. Li et al., graphene oxide may begin to decompose at approximately 70 °C [24]. Considering this indication, the whole synthesis of GO was performed at low temperature, including the GO thermal drying at 50 °C. On the other hand, the MgO–rGO nanocomposite was produced by a reflux reaction at 100 °C to enhance GO decomposition and rGO production.

2. Materials and Methods

All chemicals, including graphite powder (with diameter < 20 µm, synthetic), potassium permanganate (KMnO4), magnesium oxide (MgO), L-ascorbic acid (99%), DPPH radical (2,2-diphenyl-1-picrylhydrazyl radical), sulfuric acid (95–97%), hydrogen peroxide, N,N-Dimethylformamide (DMF),ammonium molybdate, and methanol were purchased from Sigma-Aldrich (Sigma-Aldrich, St. Louis, MO, USA). Starting materials were used as received, without any further purification.

2.1. GO Synthesis

GO powder was obtained using a novel modified Hummers’ synthesis protocol according to our previous work [17]. Based on the graphite: KMnO4 ratio, three samples named GO1:2, GO1:3, and GO1:4 were synthesized. Scheme 1 shows the main steps of GO synthesis. In the 2nd step, the obtained GO samples were simultaneously reduced and decorated with MgO to obtain magnesium oxide-decorated reduced graphene oxide (MgO–rGO).

2.2. MgO–rGO Synthesis

The reduction and decoration of graphene oxide with (MgO) were carried out by reflux reaction in diluted DMF solution. Briefly, we added 500 mg of GO dispersed in 8.3 mL of distilled water to an equal amount of magnesium hydroxide (500 mg) dispersed in 75 mL of DMF (These two dispersions, before mixing, were sonicated for 30 min). The reflux reaction was carried out at 100 °C for 2 h. The final product was collected after washing, centrifugation (4000 rpm, 5 min), and drying in an air oven (50 °C during 36 h). Figure 1 represents the principal steps of MgO–rGO nanocomposites synthesis. No other treatments were applied to the obtained samples before characterization.

2.3. Antioxidant Activity

All in vitro antioxidant assays were performed using Shimadzu UV-1280 spectrophotometer using the appropriate photon wavelengths. Data were analyzed intriplicate and expressed as mean ± SD using Microsoft Excel 2010.

2.3.1. DPPH Radical Scavenging Assay

The free radical scavenging activity of tested nanocomposites was determined using the stable radical DPPH (2,2-diphenyl-1-picrylhydrazyl) and ascorbic acid as a standard [25]. A total of 0.1 mL of different concentrations (100, 200, and 400 µg/mL) of synthesized nanocomposites was mixed with a 1.9 mL freshly prepared DPPH (0.004% in methanol) solution and vortexed thoroughly. Then, the solution was incubated at room temperature in the dark for 30 min. The absorbance was determined at 517 nm using a spectrophotometer blanked with methanol. The DPPH radical scavenging activity was calculated by the following Equation (1):
DPPH° scavenging activity (%) = [(Abs C − Abs S)/(Abs C)] ×100
where Abs C is the absorbance of the control and Abs S is the absorption of the samples and standards described below.

2.3.2. Hydrogen Peroxide Scavenging Assay

The ability of the tested nanocomposites to scavenge H2O2 was estimated by the Ruch method [26] using ascorbic acid as a standard. The nanocomposites at different concentrations were mixed with 1.4 mL phosphate buffer (0.05 M, pH 7.4) and 0.6 mL H2O2 (40 mM). The reaction mixture was vortexed and after 10 min of reaction time, its absorbance was measured at 230 nm. The ability of the nanocomposites to scavenge the H2O2 was calculated using Equation (1) formula.

2.3.3. Phosphomolybdenum Assay

The total antioxidant capacity (TAC) of tested nanocomposites was determined by the phosphomolybdate method [27] using ascorbic acid as a standard. An aliquot of 100 μL of nanocomposites solution was mixed with 400 μL methanol and 1 mL of reagent solution (0.6 M sulfuric acid, 28 mM sodium phosphate, and 4 mM ammonium molybdate), making a total volume of 1.5 mL. Sample tubes were capped and incubated in a water bath at 95 °C for 90 min. The mixture was allowed to cool to room temperature, and the absorbance was measured at 695 nm. A mixture containing distilled water served as a control. Higher absorbance indicates higher total antioxidant potential. The TAC was calculated using Equation (2) as follows:
TAC (%) = [(Abs S − Abs C)/(Abs S)] × 100
where Abs C is the absorbance of the control and Abs S is the absorption of the samples and standard.

2.3.4. Structural and Chemical Characterization

XRD patterns were recorded using Siemens D5000 Diffractometer (Bragg Brentano configuration-CuKα1, FILAB, Dijon, France). For XPS, the chemical composition of the GO and (MgO)–rGO samples were performed using an Axis DLD Ultra from Kratos (Manchester, UK) and consists of the acquisition of a wide spectrum at pass energy of 160 eV to detect all the chemical elements constituent the sample surface. High-resolution core lines were acquired at a higher energy resolution using a pass energy of 20 eV. The typical energy resolution is ~0.3 eV. Finally, data reduction was performed using software made in-house based on the R platform. For each core line, linear background subtraction and Gaussian components were used for peak fitting.

3. Results and Discussion

3.1. XRD and XPS Characterization

The synthesis of GO was performed using a modified Hummer’s method, a simple procedure without using NaNO3 in the reaction; our work is similar to the Chen et al. synthesis but without using vigorous stirring in an oil bath at 40 °C [28]. Furthermore, no acids were used during washing and centrifugation, leading to an eco-friendlier process.
Figure 2A displays the XRD spectra of graphite and GO powder obtained in our previous work by Baali et al. [17]. Spectra show a progressive disappearance of the (002) diffraction peak of graphite at 26° indicating that the best oxidation is obtained for the GO1:4 sample compared to GO1:2 and GO1:3 samples. Figure 2B shows the X-ray patterns of MgO–rGO1:2, MgO–rGO1:3, and MgO–rGO1:4 samples acquired in the 5° to 80° 2θ range. In the current synthesis, we use the same conditions used in our previous work [17]. However, XRD results show the coexistence of both MgO and Mg(OH)2 phases, as shown by the diffraction peaks relative to these distinct phases in Figure 2B. According to Purwajanti et al. [29], MgO–Mg(OH)2 decorated reduced graphene oxide nanocomposite presents superior catalytic properties compared to MgO–rGO. In particular, this work proves the higher efficiency of Mg(OH)2–rGO–MgOin water purification processes by removing arsenites. Data regarding XRD diffraction patterns of Mg(OH)2 and MgO nanocrystals are summarized in Table 1.The superposition of XRD patterns of MgO–rGO1:2, MgO–rGO1:3 and MgO–rGO1:4 do not show remarkable differences concerning phase identification except for peaks indicating the degree of oxidation or reduction, which are located near 10° (and lower than 20°) and 26°, respectively. These peaks show a small shift due to variation of oxidation or reduction extent of our graphene oxide samples.
For each obtained samples, XPS surveys were recorded in the 0 to 1350 eV range. Figure 3A reports the typical survey for the MgO–rGO1:2 nanocomposite. The main spectral peaks deriving from O 1s, C 1s, Mg 1s, and Mg 2p are indicated, as well as the Auger features relative to these elements. The more intense peaks correspond to the O 1s and Mg KLL features, followed by C 1s. For magnesium, the Mg 1s shows a much lower intensity requiring a higher integration time to acquire high-quality spectra to obtain the chemical information from the pristine and decorated materials. As for the binding energy of these spectral components, the C 1s, O 1s, and Mg 1s peaks are located at ~285.05 eV, ~533.70 eV and ~1304.34 eV, respectively. High-resolution XPS (HR-XPS) spectra were recorded for each of these elements. Figure 3B–D display the high-resolution spectra of C 1s, O 1s, and Mg 1s, together with their decomposition in various bond components. The HR-XPS spectra of C 1s were fitted using five components falling at 284.2 eV, 285.53 eV, 286.7 eV, 288.3 eV, and 290.9 eV were assigned, respectively, to the graphitic C–C, C–H, C–OH, C=O, and O=C–OH, chemical bonds. Three components were used to fit the spectrum of O 1s, which were assigned to the following bonds: Mg–OH, C=O, and C–OH situated at 531.11 eV, 532.75 eV, and 534.50 eV, respectively. As for Mg, the 1s peak was decomposed using four components relative to Mg (metal), MgO, Mg2+ adsorbed on GO, and Mg(OH)2 situated, respectively, at 1302.6 eV, 1303.7 eV, 1305.0 eV, and 1306.4 eV. Peak assignment was carried out with references to the current literature [33,34,35,36,37,38,39,40,41,42,43]. Figures S1 and S2 report the HR-XPS spectra of MgO–rGO1:3 and of MgO–rGO1:4 nanocomposites. These figures display similar spectra as those of MgO–rGO1:2, except for the disappearance of the component associated with OH bond in HR-XPS spectra of O 1s and the absence of the component related to Mg(OH)2 in the fit of Mg 1s.

3.2. Antioxidant Properties

Nanomaterials represent one of the most promising frontiers in research for improved antioxidants. Some nanomaterials, including organic or metal-based nanoparticles, exhibit intrinsic redox activity that is often associated with radical trapping [44]. A high number of tests are available for the direct measurement of the transfer of protons or the transfer of electrons from antioxidants to free radicals. A combination of different chemical methods is needed to clarify the mechanisms and kinetics of the processes at the basis of the antioxidant property of the various kinds of substances [45]. In this context, the present study explores the antioxidant properties of GO and MgO–rGO nanocomposites using DPPH radicals scavenging assay, H2O2 scavenging assay, and phosphomolybdate assay at concentrations 100, 200 and 400 μg/mL, respectively. The results of the antioxidant properties evaluation are depicted in Figure 4.
The DPPH radical was considered to be a model of lipophilic radical. Being a stable free radical, DPPH is regularly used to determine the radical scavenging activity of natural and/or synthetic compounds. In its radical form, DPPH absorbs at 517 nm and its absorbance decreases upon reduction with an antioxidant [46]. In the present study, all the tested nanocomposites had scavenging activity DPPH radicals in a dose-dependent manner, where the higher inhibition percentage was found at 400 µg/mL (Figure 4A). DPPH free radical scavenging efficacy of GO and MgO–rGO samples were in this order: ascorbic acid (95.45 ± 4.07%) > GO1:4 (40.00 ± 1.02%) > MgO–rGO1:4 (36.18 ± 0.66%) > GO1:2 (34.69 ± 3.69%) > MgO–rGO1:3 (30.58 ± 0.90%) > GO1:3 (26.06 ± 1.45%) > MgO–rGO1:2 (22.64 ± 2.15%). Antioxidants with DPPH radical scavenging activity donate hydrogen to free radicals that are the major initiators of oxidative biological and non-biological deteriorations. Earlier research illustrates the ability of the graphene-based composites in neutralizing the free radicals or peroxide decomposition by their antioxidant power [16]. As observed, there are several works in the literature regarding the synthesis and characterization of MgO–rGO nanocomposites but none on the ROS scavenging properties of MgO–rGO. The only exception is the study of MgO–GO (magnesium oxide decorated graphene oxide) by R.M. Fathy et al. [47] confirming that GO/MgO nanocomposite is effective in inhibiting the DPPH. In this work authors assessed the antioxidant activity of GO/MgO (magnesium oxide decorated graphene oxide) was assessed showing a remarkable result of 56.71% (500 µg/mL). In our work the scavenging activity of the MgO–rGO1:4 nanocomposite in H2O2 tests shows a value of 58.36 ± 5.29%. This is principally associated with an electron or proton charge transfer to DPPH radical, converting it to a yellowish stable molecule. GO conjugated with metal oxides increases their individual antibacterial and antioxidant properties.
In the H2O2 scavenging assay, H2O2 is measured as one of the major inducers of cellular aging and could attack numerous cellular energy-producing systems [48]. As in the previous assays, the tested nanocomposites exhibited concentration-dependent H2O2 scavenging activities displayed in Figure 4B.At a concentration of 400 µg/mL, the H2O2 scavenging activity of the tested nanocomposites was in the following order: Ascorbic acid (83.61 ±0.25%) > GO1:4 (58.36 ± 5.29%) > MgO–rGO1:4 (44.97 ± 1.30%) > GO1:2 (42.01 ± 3.78%) > MgO–rGO1:3 (39.06 ± 0.65%) > MgO–rGO1:2 (32.19 ± 1.05%) > GO1:3 (19.62 ± 3.60%).
A further test was performed using a phosphomolybdate assay, which has been reported to be suited to the monitoring of total antioxidant activity in the different specimens. The assay is based on the reduction of phosphomolybdate ions in presence of an antioxidant, resulting in the formation of a green phosphate/MoV complex, which is measured spectrophotometrically [49]. As displayed in Figure 4C, and in this case, the total antioxidant capacity of tested nanocomposites and standard was also dose-dependent. Increasing the concentration of the samples increased the total antioxidant effect. At a concentration of 400 µg/mL, the total antioxidant activity of the tested nanocomposites was in the following order: Ascorbic acid (85.16 ± 3.70%) > GO1:4 (42.37 ± 0.70%) > MgO–rGO1:4 (34.92 ± 3.30%) > GO1:3 (30.91 ± 2.50%) > MgO–rGO1:3 (28.79 ± 3.5%) > GO1:2 (24.61 ± 3.70%) > MgO–rGO1:2 (22.48 ± 1.05%). In all the three tests GO1:4 showed the higher antioxidant ability followed by MgO–rGO1:4. This may be explained by the fact that the transfer of electrons/hydrogen from antioxidants depends on their nanocomposite structure. Noticeably, the scavenging activity observed with MgO–rGO1:4 nanocomposite might be due to the synergetic effect between MgO nanoparticles and GO [47,50].

4. Conclusions

This work illustrates the synthesis and structural characterization and antioxidant assessment of MgO–rGO nanocomposite. The aim is to fill a literature gap being the scavenging activity of MgO–rGO nanocomposites still not analyzed in detail. For this reason, three different GO samples obtained using (1:2), (1:3) and (1:4) graphite: KMnO4 mass ratios, were used as a host matrix for MgO nanoparticles.
-
Structural characterization of the obtained product, using X-ray diffraction confirms the formation of Mg(OH)2 phase in addition to MgO nanoparticles, resulting in a MgO–rGO–Mg(OH)2 nanocomposite.
-
XRD spectra of MgO–rGO1:2, MgO–rGO1:3, and MgO–rGO1:4 samples show the typical diffraction peaks of magnesium oxide and magnesium hydroxide. These diffraction peaks display a clear broadening, informing us about the nanometric size of Mg(OH)2 and MgO nanoparticles.
-
All XPS wide spectra of the MgO–rGO nanocomposite show peaks related to C 1s, O 1s, and Mg 1s. The peak fitting of the high-resolution O 1s and Mg 1s core lines relative to the MgO–rGO1:4 and MgO–rGO1:3 samples display components related to MgO and Mg(OH)2. However, this latter component disappeared in the O 1s and Mg 1s spectra of the MgO–rGO1:2 nanocomposite. This is in agreement with the structural characterization results confirming the formation of nanocomposite MgO–rGO–Mg(OH)2.
-
The synthesized samples, i.e., GO1:2, GO1:3, GO1:4, MgO–rGO1:2, MgO–rGO1:3, and MgO–rGO1:4 nanocomposites were screened for antioxidant activity using DPPH radicals scavenging assay, H2O2 scavenging assay, and phosphomolybdate assay. The results suggest significant antioxidant activity in a concentration-dependent manner. Among the different synthesized nanoparticles, GO1:4 and MgO–rGO (1:4) showed the best antioxidant activity in all assays carried out. Current results suggest that GO1:4 is an excellent platform for radical-trapping antioxidants and could be useful as an antioxidant in environmental and pharmaceutical applications.
The remarkable results obtained in this work encourages us to further explore the MgO–rGOnanocomposite antioxidant properties in living cells and animal assays. If results are confirmed, considering the potentialities of this nanoparticulate, interesting perspectives for applications in biomedicine to combat the adverse effects of free radicals will be opened.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/c8040049/s1, Figure S1. XPS Spectra of MgO–rGO1:3 nanocomposite. Survey spectrum (A), and high-resolution spectra of C1s (B), O1s (C), and Mg1s (D). Figure S2. XPS Spectra of MgO–rGO1:4 nanocomposite. Survey spectrum (A), and high resolution spectra of C1s (B), O1s (C), and Mg1s (D).

Author Contributions

Conceptualization and methodology: A.B., N.B. and R.B.; formal analysis, investigation, and resources: A.B., N.B. and G.S.; writing—original draft preparation: A.B. and N.B.; writing—review and editing: A.B., N.B. and G.S. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported partially by the Ministry of Higher Education and Scientific Research—Algeria (MESRS) and the Ministry of Foreign Affairs and International Cooperation of Italy; Bilateral Algerian-Italian research project AL16MO06.

Acknowledgments

We are grateful to Abdelmalek Bouraiou from Chemistry Department–Mentouri Brothers University for laboratory facilities.

Conflicts of Interest

The authors declare no conflict of interest.

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Carbon 08 00049 sch001 550
Scheme 1. GO synthesis procedure.
Scheme 1. GO synthesis procedure.
Carbon 08 00049 sch001
Carbon 08 00049 g001 550
Figure 1. GO and MgO–rGO nanocomposites synthesis steps: (1) Separate sonication of DE:GO and DMF:HMg solutions; (2) MgO–rGO reflux synthesis (a—stirrer, b—flask, c—cooler, d—temperature regulator); (3) MgO–rGO solution (A) and MgO–rGO powder after washing and centrifugation (B).
Figure 1. GO and MgO–rGO nanocomposites synthesis steps: (1) Separate sonication of DE:GO and DMF:HMg solutions; (2) MgO–rGO reflux synthesis (a—stirrer, b—flask, c—cooler, d—temperature regulator); (3) MgO–rGO solution (A) and MgO–rGO powder after washing and centrifugation (B).
Carbon 08 00049 g001
Carbon 08 00049 g002 550
Figure 2. X-ray patterns of synthetized nanocomposites: (A) graphite and (GO1:2, GO1:3, and GO1:4) samples; (B) MgO–rGO1:2, MgO–rGO1:3, and MgO–rGO1:4 samples.
Figure 2. X-ray patterns of synthetized nanocomposites: (A) graphite and (GO1:2, GO1:3, and GO1:4) samples; (B) MgO–rGO1:2, MgO–rGO1:3, and MgO–rGO1:4 samples.
Carbon 08 00049 g002
Carbon 08 00049 g003a 550Carbon 08 00049 g003b 550
Figure 3. XPS Spectra of MgO–rGO1:2 nanocomposite. Survey spectrum (A), C 1s (B), O 1s (C) and Mg 1s (D) high-resolution spectra.
Figure 3. XPS Spectra of MgO–rGO1:2 nanocomposite. Survey spectrum (A), C 1s (B), O 1s (C) and Mg 1s (D) high-resolution spectra.
Carbon 08 00049 g003aCarbon 08 00049 g003b
Carbon 08 00049 g004 550
Figure 4. Antioxidant activity of pure graphene oxide (GO), MgO-decorated reduced graphene oxide (rGO) and ascorbic acid at different concentration range (100, 200, and 400 µg/mL) (n = 3): (A) DPPH radical scavenging activity; (B) H2O2 scavenging activity; (C) total antioxidant activity.
Figure 4. Antioxidant activity of pure graphene oxide (GO), MgO-decorated reduced graphene oxide (rGO) and ascorbic acid at different concentration range (100, 200, and 400 µg/mL) (n = 3): (A) DPPH radical scavenging activity; (B) H2O2 scavenging activity; (C) total antioxidant activity.
Carbon 08 00049 g004
Table
Table 1. XRD peak identification of MgO–rGO nanocomposite.
Table 1. XRD peak identification of MgO–rGO nanocomposite.
Phase2θ (°) Crystalline Structure(hkl)References
Mg(OH)218.49exagonal (Brucite lamellar)
(JCPDS: 00-007-0239)		001[29,30]
32.86100
38.01101
50.72102
58.6110
68.21103
72.01201
MgO42.88Cubic (fcc) (JCPDS 87-0653)200[31,32]
62.12220
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Bensouici, A.; Baali, N.; Bouloudenine, R.; Speranza, G. Decoration of Reduced Graphene Oxide with Magnesium Oxide during Reflux Reaction and Assessment of Its Antioxidant Properties. C 2022, 8, 49. https://doi.org/10.3390/c8040049

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Bensouici A, Baali N, Bouloudenine R, Speranza G. Decoration of Reduced Graphene Oxide with Magnesium Oxide during Reflux Reaction and Assessment of Its Antioxidant Properties. C. 2022; 8(4):49. https://doi.org/10.3390/c8040049

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Bensouici, Aicha, Nacera Baali, Roumaissa Bouloudenine, and Giorgio Speranza. 2022. "Decoration of Reduced Graphene Oxide with Magnesium Oxide during Reflux Reaction and Assessment of Its Antioxidant Properties" C 8, no. 4: 49. https://doi.org/10.3390/c8040049

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