Sustainable gamma irradiation strategy for GO and rGO modification: Impact on electromagnetic interference shielding efficiency

Sustainable gamma irradiation strategy for GO and rGO modification: Impact on electromagnetic interference shielding efficiency Jovana Prekodravac Filipovic a,* , Mila Milenkovic a , Duska Kleut a , Kamel Haddadi b , Muhammad Yasir c , Warda Saeed c , Danica Bajuk Bogdanovic d , Svetlana Jovanovic a a Vinˇ ca Institute of Nuclear Sciences, National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia b University of Lille, CNRS, Centrale Lille, University Polytechnique Hauts-de-France, UMR 8520-IEMN-Institut d’Electronique de Micro´ electronique et de Nanotechnologie–Lille, France c Department of Computer Science, Division of Microrobotics and Control Engineering, University of Oldenburg, Oldenburg, Germany d Faculty of Physical Chemistry, University of Belgrade, Belgrade, Serbia ARTICLE INFO Keywords: Graphene oxide Reduced graphene oxide Gamma irradiation Electromagnetic interference Shielding ABSTRACT Electromagnetic interference (EMI) has emerged as a significant issue in contemporary electronic systems, particularly within aerospace, defense, and communication technology. Graphene-derived materials, including graphene oxide (GO) and reduced graphene oxide (rGO), present remarkable potential for lightweight, flexible, and EMI shielding solutions owing to their adjustable electrical conductivity and structural integrity. This study introduces an eco-friendly method for adjusting the EMI shielding effectiveness (EMI SE) of free-standing films made from GO and rGO by controlled gamma irradiation at low (50 kGy) and high (300 kGy) doses, conducted in two types of media: air and isopropyl alcohol (IPA). The structural alterations generated by irradiation were characterized by Raman and Infrared spectroscopies, X-ray diffraction (XRD), scanning electron microscopy (SEM), and contact angle measurements, indicating changes in defect density, surface roughness, and hydrophilicity. Results indicate that gamma irradiation can precisely adjust the oxidation/reduction equilibrium, hence boosting conductivity in rGO and improving interfacial polarization in GO. Remarkably, rGO films exposed to air demonstrated exceptional EMI SE values above 20 dB in the X-band (8–12 GHz), signifying their suitability for advanced shielding applications. This research illustrates the effectiveness of gamma irradiation as an environmentally friendly, scalable method for modifying the characteristics of graphene-based materials, facilitating their incorporation into advanced aeronautical and electronic equipment. 1. Introduction The emergence of new environmental pollution issues, including electromagnetic pollution and electromagnetic interference (EMI) from electrical and electronic devices, has significantly escalated due to the swift advancement of information technology. Electronics and their components, characterized by increased power, reduced size, and enhanced operational speed, create undesirable electromagnetic waves that can cause malfunction and deterioration of devices, as well as pose risks to human health and the environment [40,49]. Graphene oxide (GO) and reduced graphene oxide (rGO) have recently emerged as highly promising carbon-based nanomaterials because to their remarkable structural, thermal, and electrical properties [29,43,48]. GO, a highly oxidized variant of graphene, is abundant in oxygen-containing functional groups that confer hydrophilicity and facilitate effortless dispersion in water and other solvents. Upon reduction, GO is largely transformed into rGO, restoring sp² hybridized carbon network, thus improving its electrical conductivity while preserving some functional groups that enhance structural plasticity. The distinctive properties of GO and rGO render them appealing for numerous advanced technical applications, especially in electronics, sensing, energy storage, and EMI shielding [18,27,36,45,54]. The capacity to produce free-standing films of GO and rGO is a vital advancement for their practical incorporation into gadgets. Such films provide flexibility, scalability, and mechanical durability without requiring supporting substrates. Conventional methods, such as * Corresponding author at: Vinˇ ca Institute of Nuclear Sciences, National Institute of the Republic of Serbia, University of Belgrade, Mike Petrovica Alasa 12-14, Vinca, Belgrade 11351, Serbia. E-mail address: [email protected] (J.P. Filipovic). Contents lists available at ScienceDirect Chemical Engineering Journal Advances journal homepage: www.sciencedirect.com/journal/chemical-engineering-journal-advances https://doi.org/10.1016/j.ceja.2025.100873 Chemical Engineering Journal Advances 24 (2025) 100873 Available online 16 September 2025 2666-8211/© 2025 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ ). Langmuir-Blodgett [55], wet spinning [28], spray coating [37] etc., frequently have contamination issues or restricted scalability [11]. The strong Van der Waals interactions between GO and various substrates result in significant adhesion, making the separation of GO films from these substrates particularly challenging. As a result, there is an increasing demand for cost-effective substrates that allow facile removal without leaving behind residues or causing structural damage to the GO films. Conversely, membrane-assisted casting processes offer a hygienic, economical, and consistent approach for generating homogenous, flexible, and substrate-free films [33]. These films can subsequently undergo post-treatment, such as chemical or radiation-induced reduction, to modify their characteristics for particular purposes. Gamma irradiation, commonly employed in the sterilization of medical or scientific equipment, has been utilized to alter the physicochemical properties of carbon-based materials at the nanoscale [2]. Gamma irradiation is a high-energy processing method that employs photons, typically from Co 60 , which penetrate deeply into materials and transfer energy through ionization and excitation. This process generates secondary electrons and reactive species that can cleave chemical bonds, form radicals, and initiate oxidation or reduction depending on the surrounding atmosphere and medium. In oxygen-rich environments, irradiation promotes oxidative pathways and the formation of oxygenated groups, whereas under inert atmospheres or in aqueous suspensions with radical scavengers, reductive chemistry dominates, removing oxygen functionalities and restoring conjugated structures [25]. The effects of gamma irradiation are significantly influenced by the irradiation conditions, such as total dose, dose rate, atmosphere, temperature, the nature of materials, and the irradiation medium which collectively determine whether crosslinking, chain scission, oxidation, or reduction will prevail. A plethora of instances demonstrating various (or even contradicting) outcomes following irradiation under diverse situations is available in the literature [51]. Concerning graphene, gamma irradiation in various liquid media, has been effectively employed for the oxidation/reduction of GO and rGO [7,13,52]. In the context of graphene oxide, gamma irradiation has been widely used as a green and scalable method to tune its chemistry: in air or oxygenated systems irradiation can increase oxidation or introduce defects, while in inert environments or aqueous suspensions containing alcohols that scavenge oxidizing radicals, it efficiently reduces GO by removing epoxide, hydroxyl, and carboxyl groups and partially restoring sp² domains. Proper dose control is critical, as moderate irradiation enhances the C/O ratio and conductivity, but excessive doses can damage the carbon lattice and generate structural defects. Thus, gamma irradiation provides a controllable, chemical-free route for the oxidation or reduction of graphene oxide, enabling the production of reduced graphene oxide with tailored properties for electronic, catalytic, and environmental applications [56]. One of the potential applications of carbon-based nanomaterials is EMI shielding. Owing to their superior electrical conductivity and layered architecture, carbon-based nanomaterials demonstrate exceptional attenuation of electromagnetic waves over a broad frequency spectrum [9,46]. EMI shielding is essential in contemporary electronics and communication technologies, particularly within the aerospace industry, where weight, durability, and performance under harsh conditions are critical considerations. Moreover, the inherent resistance of GO and rGO to ionizing radiation—particularly when subjected to processes like gamma irradiation—positions them as formidable prospects for applications in aeronautical and astronomical technology, where materials must endure severe radiation conditions. This paper introduces a systematic method for producing highly flexible, contamination-free, free-standing films of GO and rGO utilizing membrane filters as detachable substrates. The films were further subjected to various gamma irradiation doses in two different environments - air and isopropyl alcohol (IPA), to induce structural modifications and enhance their electromagnetic interference shielding effectiveness (EMI SE). The rGO films exhibited significantly enhanced EMI SE values exceeding 20 dB, in contrast to the GO films, which demonstrated much lower effectiveness (ranging from 0.31 dB to 0.52 dB). The findings suggest that gamma irradiation can introduce sufficient structural modification to promote EMI SE, but jet again it does not substantially alter the structural integrity of the materials, highlighting their robustness and suitability for demanding applications such as aerospace and astronomical technologies. Therefore, the aim of the work is to develop a systematic approach for fabricating flexible, contamination-free, freestanding GO and rGO films using membrane filters as detachable substrates, and to investigate the influence of gamma irradiation under different environments on their structural properties and electromagnetic interference shielding effectiveness, with the goal of producing robust, high-performance materials suitable for advanced applications such as aerospace and astronomical technologies. 2. Materials and methods 2.1. Preparation of free-standing films of GO and rGO GO was synthesized by chemical oxidation of graphite using a modified Hummers’ method [6]. Initially, 1 g of graphite powder (TIMREX® Z-346 KS6, Bodio, Switzerland) was added to 23.3 mL of concentrated sulfuric acid (Carl Roth, Karlsruhe, Germany) at 4 ◦C. While stirring, 3 g of potassium permanganate (Merck, Darmstadt, Germany) was slowly introduced in small amounts. The mixture was kept under stirring for 30 min for thorough mixing and reaction initiation. Subsequently, it was gently heated to 40 ◦C. Following the addition of 50 mL of demineralized water, the mixture was kept at that temperature for 30 min. Following the addition of 50 mL demineralized water, the mixture was stirred at 95 ◦C for 15 min. Subsequently, 166.7 mL of water was added, followed by the slow addition of 5 mL of 30 % hydrogen peroxide, resulting in a color change from dark brown to yellow. The mixture was maintained at 95 ◦C for an additional 15 min and then cooled to room temperature. The suspension was filtered, washed with 83.3 mL of diluted HCl (1:10), dispersed in 200 mL of water and purified by dialysis (MWCO 8000–14,000 g mol -1 ) for seven days. Finally, the dispersion was sonicated and centrifuged at 3000 rpm in order to isolate GO. The resulting GO dispersion was diluted with demineralized water to 1 mg mL -1 and used for film fabrication. GO thin layers were formed by sonicating 22.5 mL of an aqueous GO suspension for 30 min, followed by vacuum-assisted filtration using a 0.22 μ m pore-size hydrophilic polycarbonate membrane (Isopore™, GTTP02500, Merck). Uniform pressure generated by the vacuum allowed for even GO layer formation. After filtration and drying, the films were peeled from the membrane. The as-prepared thin films were subsequently subjected to reduction to obtain rGO thin films. The schematic representation of the free-standing films of GO and rGO preparation is presented in Scheme 1. To achieve chemical reduction, the GO free-standing films were treated in a 15.14 mM l-ascorbic acid aqueous medium with pH adjustment using 100 μ L of concentrated HCl (5 M). The samples were then heated at 85 ◦C for 8 h, then gently washed with deionized water and dried in the air. 2.2. Gamma irradiation of free-standing films of GO and rGO Free-standing films of GO and rGO were cut into size 11 ×22 mm, and submitted to the gamma irradiation (Co 60 source) at different dosages (50, 100, 200, and 300 kGy) in air and IPA media to promote oxidation and reduction of the surface. Due to the extent number of samples, the sample names and the corresponding conditions for their preparation are shown in Table 1. 2.3. EMI SE measurements Electromagnetic interference shielding effectiveness (EMI SE) of J.P. Filipovic et al. Chemical Engineering Journal Advances 24 (2025) 100873 2 free-standing GO samples was obtained using a vector network analyzer (VNA, a Rohde & Schwarz ZVA 24 Vector Network Analyzer, Munich, Germany). Namely, VNA was used to measure the S-parameters in the 8–12 GHz frequency range. Free-standing samples of gamma-irradiated GO were cut into a rectangular shape, 15 mm x 25 mm, to cover the WR90 waveguide adapters’ inner space. RF coaxial cables were used to connect WR-90 waveguide adapters with ports 1 and 2 of the VNA. The gamma irradiated GO films were positioned between the 2 waveguide adapters, and the values of S scattering parameters were collected, as previously reported [26]. The total shielding effectiveness was estimated using Eqs. (1)–(3) [3, 32]: SE =LD+LM(1) where SE is the sum of dissipation loss L D , and mismatch loss L M . The L M is calculated using relation (2): LM= − 10log10(1− |S11|2)(2) To obtain the value of L D , the reflection scattering parameter, S 11 , and transmission scattering parameter, S 21 , were used (3): LD= − 10log10((|S21|2)/(1− |S11|2)(3) Parameters S 11 and S 21 were collected by using a VNA. 2.4. Materials characterization We employed the INCAx-act LN2-free analytical silicon drift detector for SEM-EDS, featuring PentaFET® Precision and the Aztec 4.3 software package (Oxford Instruments, Oxfordshire, UK), linked to a TESCAN Mira3 XMU operating at 20 kV with a secondary electron detector. BP and BG powders were applied to the conductive double-sided adhesive. Raman spectra of samples were obtained by a DXR Raman microscope (Thermo Scientific) using a 532 nm laser as an excitation source. The laser power was kept at 2 mW to avoid heating of the sample with a pixel-to-pixel spectral resolution of 1 cm -1 . Fourier-transform infrared (FTIR) spectra were recorded using a Nicolet iS20 FTIR spectrometer (Thermo Scientific) equipped with an ATR accessory featuring a diamond crystal. Measurements were performed in the range of 4000–525 cm⁻¹, using 16 scans per sample and a spectral resolution of 4 cm⁻¹. Prior to each measurement, the ATR crystal was thoroughly cleaned to avoid contamination. The samples were analyzed directly, without any additional chemical preparation, by pressing them onto the crystal surface. 3. Results and discussion 3.1. SEM/EDS investigation The surface morphology of pristine and gamma-irradiated GO samples was investigated using SEM analysis. The top view image (Fig. 1a) of GOp shows a uniform distribution of the GO sheets on a large scale with rough and wavy surface, while under gamma treatment (GO_air_50 kGy) in air (Fig. 1b) the surface becomes more corrugated. Further increase in gamma dosage (Fig. 1c, d) caused the formation of loose GO sheets on top of the free-standing films surface probably as a result of the oxidation process, while irradiation at 300 kGy (Fig. 1e) influenced the morphology by arranging the surface in a more organized structure. The reduction in IPA (Fig. 1h-j) affected the GO surface by providing more flattened morphology, when compared to the GOp, with agglomerate formation as a result of the surface disturbance by reduction. Once again, in a sample GO_IPA_300 kGy (Fig. 1j), a more arranged surface was observed. In the rGO samples, a more wrinkled or wavy morphology (Fig. 2) was detected when compared to the GO samples which can be a result of several dominating factors. By removing oxygen functional groups, the establishment of π - π interaction between graphene sheets is occurs [17,38]. The top-view image (Fig. 2a) of rGOp exhibits a homogeneous distribution of rGO sheets on a wide scale, characterized by a rough and undulating surface. In contrast, following gamma treatment in air (Fig. 2b-e), the surface becomes increasingly corrugated with agglomerate formation as a result of the surface disturbance. This is probably due to the formation of loose rGO sheets on top of the free-standing film’s surface as a result of the oxidation process [5]. With an increase in the gamma irradiation dosage from 50 to 300 kGy, a more disturbed surface was noticed. In the reduction medium (Fig. 2g-j), improvement of the surface roughness and waviness was observed. The increased waviness in rGO free-standing films, when compared to GO, mostly results from structural relaxation, defect reduction, and the loss of planar alignment, which is often preserved in the more Scheme 1. Three steps for production of free-standing films of GO and rGO. Table 1 List of samples and induced gamma dosages. Source Medium Gamma irradiation dosage (kGy) Sample name GO - - GOp GO air 50 GO_air_50kGy GO air 100 GO_air_100kGy GO air 200 GO_air_200kGy GO air 300 GO_air_300kGy GO IPA 50 GO_IPA_50kGy GO IPA 100 GO_IPA_100kGy GO IPA 200 GO_IPA_200kGy GO IPA 300 GO_IPA_300kGy rGO - - rGOp rGO air 50 rGO_air_50kGy rGO air 100 rGO_air_100kGy rGO air 200 rGO_air_200kGy rGO air 300 rGO_air_300kGy rGO IPA 50 rGO_IPA_50kGy rGO IPA 100 rGO_IPA_100kGy rGO IPA 200 rGO_IPA_200kGy rGO IPA 300 rGO_IPA_300kGy J.P. Filipovic et al. Chemical Engineering Journal Advances 24 (2025) 100873 3 hydrophilic and functionalized GO. In the reduction of GO to rGO, oxygen-containing functional groups, including hydroxyl, carboxyl, and epoxide, are eliminated. These groups enhance interlayer spacing and planar stability in GO. Their elimination disrupts regularity and induces heightened structural disorder, culminating in a more wrinkled or undulating morphology [5]. The reduction process partially reinstates the sp² carbon network, albeit incompletely. This incomplete repair generates internal stress and localized imperfections, resulting in the bending or rippling of the nanosheets in the final film configuration. During the processes of film formation and solvent evaporation, the more hydrophobic rGO sheets exhibit distinct aggregation and collapse behaviors compared to the hydrophilic GO sheets. This frequently leads to folding and wrinkling, imparting a more textured surface to rGO films. The elimination of oxygen groups during reduction frequently results in a volumetric contraction, which may induce mechanical stress and deform the planar structure, hence causing waviness. The EDX analysis results of the oxidation/reduction processes of GO and rGO are presented in Table 2. From the EDX results we confirmed the presence of both O and C atoms in both samples (GO and rGO) but with variations in the atomic %. Oxidation/reduction of GO in air and IPA did not significantly influence the C at % or O at % significantly, but rather small shifts were noticed. This could be the consequence of a layered structure of the freestanding films, a highly oxidized surface of GO, and low gamma irradiation energy to efficiently make significant changes on the GO surface. Gamma irradiation in air generates oxidizing radicals (like • OH and O₂ • ⁻), which can re-oxidize GO or prevent the full reduction process. Oxygen in air rapidly reacts with hydrated electrons and radicals, Fig. 1. SEM/EDS analysis of GO treated under different gamma irradiation dosages: a) GOp, b) GO_air_50 kGy, c) GO_air_100 kGy, d) GO_air_200 kGy, e) GO_air_300 kGy, f) statistical representation of the C at % and O at % based on the EDS analysis, g) GO_IPA_50 kGy, h) GO_IPA_100 kGy, i) GO_IPA_200 kGy, and j) GO_IPA_300 kGy. Fig. 2. SEM/EDS analysis of rGO treated under different gamma irradiation dosages: a) rGOp, b) rGO_air_50 kGy, c) rGO_air_100 kGy, d) rGO_air_200 kGy, e) rGO_air_300 kGy, f) statistical representation of the C at % and O at % based on the EDS analysis, g) rGO_IPA_50 kGy, h) rGO_IPA_100 kGy, i) rGO_IPA_200 kGy, and j) rGO_IPA_300 kGy. J.P. Filipovic et al. Chemical Engineering Journal Advances 24 (2025) 100873 4 reducing the availability of reducing agents that could target GO oxygen groups. On the other hand, IPA does produce some reducing species, but not as effectively as water would with a reducing scavenger [14]. The balance between reducing and oxidizing species in IPA +air favors mild or partial reduction. Also, some oxygen groups, especially carboxylic acids at the edges, are chemically more stable and require stronger reduction conditions to be removed. In the rGO samples, a more pronounced reduction effect than oxidation was seen in both media (air, IPA) compared to rGOp (Table 2). This phenomenon can be understood through the interaction between the properties of the original materials, radiation chemistry, and the characteristics of the surrounding media. The rGO possesses a reduced amount of oxygen-containing functional groups in compared to GO. Consequently, under gamma irradiation, the reactive oxygen species or radiolytic entities produced in air or IPA may have few available oxidation sites, leading to restricted oxidation. Thus, the radiationinduced elimination of residual oxygen groups prevails, enhancing further reduction. Gamma rays produce secondary electrons and induce bond cleavage. In rGO, residual C–O, C =O, or O–C =O groups are prone to cleavage upon irradiation. This leads to deoxygenation rather than the production of new oxygen groups. In IPA, radiolysis generates reducing species, and these reducing radicals are more efficient at eliminating oxygen-containing groups, especially in previously reduced rGO, hence improving the reduction process. As a result, rGO can continue to experience significant bond scission and deoxygenation, rendering reduction the prevailing process. 3.2. FTIR investigation The FTIR characterization was used to characterize different functional groups of GO and rGO materials. The GOp showed a typical FTIR Table 2 EDX analysis of the oxidation/reduction processes of GO and rGO samples under irradiation. Sample C atomic % O atomic % Sample C atomic % O atomic % GOp 66.8 33.2 rGOp 81.6 18.4 GO_air_50 kGy 66.9 33.1 rGO_air_50 kGy 84.47 15.53 GO_air_100 kGy 67.7 32.3 rGO_air_100 kGy 83.74 16.26 GO_air_200 kGy 67.1 32.9 rGO_air_200 kGy 81.14 18.86 GO_air_300 kGy 67.2 32.8 rGO_air_300 kGy 80.6 19.4 GO_IPA_50 kGy 67.6 32.4 rGO_IPA_50 kGy 84.87 15.13 GO_IPA_100 kGy 67.8 32.2 rGO_IPA_100 kGy 85.19 14.81 GO_IPA_200 kGy 68.6 31.4 rGO_IPA_200 kGy 84.48 15.52 GO_IPA_300 kGy 68 32 rGO_IPA_300 kGy 85.9 14.1 Fig. 3. The FTIR spectra of GO and rGO treated under different gamma irradiation dosages (50, 100, 200, and 300 kGy): a) GO in air, b)GO in IPA, c) rGO in air, and d) rGO in IPA. J.P. Filipovic et al. Chemical Engineering Journal Advances 24 (2025) 100873 5 spectrum for GO (Fig. 3, black curve) with bands located in a range from 2500 to 3500 cm -1 due to carboxyl O – H stretching, 1716 cm -1 from C = O of carboxyl groups, 1609 cm -1 from C =C stretching of unoxidized graphitic domains, 1222 cm -1 from C – OH stretch of alcohol group and 1036 cm -1 from C – O stretch of C – O-C [16]. Upon oxidation in air under different gamma irradiation dosages, the band intensities were reduced, where the lowest intensities were noticed in samples treated at 200 and 300 kGy (Fig. 3a). Upon reduction in IPA (Fig. 3b), the intensities of the peaks associated with the oxygen-containing functions of GO were diminished in comparison to the peak intensities of GOp. This demonstrated the effective reduction of GO by gamma irradiation. However, the peaks did not diminish, suggesting that GO was not entirely reduced by gamma irradiation, indicating the persistence of certain functional groups [15,44]. In a case of rGO samples, the pristine rGO showed as the most prominent band the one from C =C of unoxidized graphitic domains located at 1603 cm -1 (Fig. 3c, black curve), confirming the rGO material under gamma treatment, without any oxygenated functional groups. Upon oxidation, the band at 1603 cm -1 gets more prominent, suggesting a more arranged surface of the rGO upon irradiation, while the rise of the small band at 1224 cm -1 suggest the presence of C – OH stretch of alcohol groups (Fig. 3c). The same observations were noticed for the reduced samples (Fig. 3d) with the addition of a wide band in a range from 2500 to 3500 cm -1 from the carboxyl O – H stretching mode in samples rGO_IPA_50 kGy and rGO_IPA_100 kGy. 3.3. Raman investigation Raman spectra of the free-standing highly flexible GO and rGO films, treated at different gamma irradiation dosages in air and IPA medium, with detailed analysis are shown in Fig. 4 and 5, respectively. Raman spectra of all samples show the broad/intense D band at ~1343 cm -1 , and G band at ~1590 cm -1 as well as low intensity 2D band at ~2700 cm -1 merged with D +G band (Fig. 4a,b, and Fig. 5a,b) [19]. To calculate the I D /I G and I 2D /I G ratios and establish the peak positions and FWHM, deconvoluted Raman spectra (Fig. S1, Fig. S2, Fig. S3, Fig. S4) were utilized [10]. For all GO samples irradiated in air and IPA, Raman spectra (Fig. S1, Fig. S2) were deconvoluted with 4 +3 or 3 +3 peaks assigned as A, D, G, B, 2D, D +G and 2D’, where the presence of A, B and 2D’ bands contribute to the defect level of the material which were noted mostly in oxidized samples [12]. In rGO samples, there were no additional A and B defect bands, but aside from D, G, 2D, D +G, and 2D’ bands, occasionally the D’ band was noticed, with deconvolution with mostly 2 +2 and 2 +3 bands (Fig. S3, Fig. S4). In the GO samples, the D and G band positions have not changed upon gamma irradiation, while the full width at half maximum (FWHMГ ) values have dropped. The FWHM of the D band ( Г D ), decreased when compared to GOp in air and IPA medium (Fig. 4c) which can be a confirmation of the effect of gamma irradiation on the structural changes on a nano level, particularly related to defect density and disorder in the carbon lattice in GO material. A narrower D band indicates a greater uniformity in defect types and the development of larger and more organized sp² domains, regardless of the persistence of some defects such as edge-like defects with a narrower vibrational signature. The Г G values (Fig. 4d) mostly manifest a decrease, suggesting a possible small restoration of graphitic structure and increased crystallinity. Only samples GO_air_100 kGy and GO_air_200 kGy showed an increase in a Г G values, as a result of the greater structural disorder and disturbance in sp² domains caused by oxidation. The I D /I G and I 2D /I G ratios of GO samples in air and IPA increase upon oxidation/reduction as an outcome of the surface changes (Fig. 4e, f). The disruption of the sp² domains increases the number of sp³-hybridized defects, and as a consequence, dband intensity increases and consequently I D /I G ratio. Gamma irradiation can also promote reorganization resulting in a more pronounced 2D band in comparison to the G band, leading to higher values of I 2D /I G . Raman spectra of rGO free-standing films, both pristine and treated under gamma irradiation in air and IPA, are presented in Fig. 5a,b. In both cases, a presence of D +G band was noticed, in addition to common D, G, and 2D bands. The deconvolution The decrease in the FWHM of the D ( Г D ) and G ( Г G ) bands in freestanding films of rGO following gamma irradiation, when compared to rGOp, indicates enhanced structural order and diminished defect density (Fig. 5c, d) [10]. A reduction in the Г D point to a more uniform distribution of imperfections or a drop in defect density. Gamma irradiation effect may also result in the elimination of certain oxygen functional groups and the partial reconstitution of sp² carbon networks, which can restore the lattice, leading to narrower D bands. The G band is associated with C–C bond stretching in sp² carbon regions. Therefore, a reduced Г G signifies a more consistent and organized sp² domain structure. By calculating the I D /I G ratio, an increase in values was observed in both oxidized and reduced samples (Fig. 5e). Oxidation introduces epoxy, hydroxyl, carbonyl, and carboxyl groups to the surface of rGO. These groups disturb the conjugated sp² hybridized carbon framework, transforming some sp² carbons into sp³-hybridized sites. The following disrupts the π -conjugation, resulting in more localized defects. The gamma irradiation and incorporation of functional groups also induce local strain, bending, and distortion of the graphene sheet, leading to the production of topological defects. Additionally, oxidation could damage carbon atoms at the boundaries or within the lattice, creating vacancies and dangling bonds. Upon reduction, the elevation in defect levels in rGO upon reduction is mainly attributable to the incomplete and frequently incomplete elimination of oxygen-containing groups and the disturbance of the carbon lattice during the reduction process (Fig. 5e). Although reduction seeks to reinstate the graphene-like structure by eliminating functional groups, it frequently creates novel defect types [10]. 3.4. XRD measurements For the XRD measurements we have chosen GOp and rGOp samples, as well as samples irradiated at high gamma dosage of 300 kGy (GO_air_300 kGy, GO_IPA_300 kGy, rGO_air_300 kGy, and rGO_IPA_300 kGy). The GOp sample shows the characteristic low-angle (001) reflection at ~11.82◦(2θ), associated with expanded interlayer spacing produced by oxygen functional groups and intercalated water (Fig. S5). This peak is relatively sharp compared with the irradiated GO spectra, indicating more regular lamellar stacking [31,34]. By contrast, when GO is irradiated in IPA the XRD evolution indicates reductive deoxygenation and restacking. At high dose such as 300 kGy, the GO (001) peak markedly attenuates and a broader (002)-type feature grows near the graphitic region (~22.87◦), signifying removal of oxygen groups, expulsion of intercalated water, and partial recovery of closer sp² stacking. The IPA medium promotes reducing radiolytic species (solvated electrons, H•) and scavenges •OH, which explains the trend toward deoxygenation and the appearance of graphitic (002) intensity in IPA-irradiated GO. When GO is γ-irradiated in air, the XRD pattern evolves in a way consistent with additional oxidative modification and disorder. At the high dose of 300 kGy, the (001) peak diminishes due to radiation-induced oxidation and defect generation, disrupting regular stacking and increasing structural disorder [34]. The rGOp lacks the prominent low-angle (001) GO peak and instead exhibits a broader, weaker feature near the higher-angle position typical of graphitic (002) stacking at ~25.07◦(2θ) (Fig. S5) [22,57]. It reflects partial restoration of sp² domains and closer interlayer spacing with residual turbostratic disorder. Upon irradiation in IPA at high dose (300 kGy) defect creation (vacancies, holes, edge damage) can broaden and reduce the (002) intensity despite low oxygen content. When rGO is irradiated in air, oxidative attack and generation of surface defects dominate: the (002) feature broadens and may shift, and background scattering increases, indicating lattice disruption and partial re-oxidation/functionalization or increased turbostratic disorder [1]. J.P. Filipovic et al. Chemical Engineering Journal Advances 24 (2025) 100873 6 Fig. 4. Raman analysis of GO free-standing films at different gamma irradiation dosages: a) in air, b) in IPA, c) FWHM D band, d) FWHM G band, e) I D /I G , and f) I 2D /I G . J.P. Filipovic et al. Chemical Engineering Journal Advances 24 (2025) 100873 7 Fig. 5. Raman analysis of rGO free-standing films at different gamma irradiation dosages: a) in air, b) in IPA, c) FWHM D band, d) FWHM G band, e) I D /I G , and f) I 2D /I G . J.P. Filipovic et al. Chemical Engineering Journal Advances 24 (2025) 100873 8 XRD is sensitive to long-range order. At low and intermediate doses (50, 100, 200 kGy), based on our previous experience, the structural changes in GO/rGO are relatively subtle. The interlayer peak broadening and intensity decrease are progressive but not dramatic, so the differences between consecutive doses are not easily distinguishable in XRD patterns. On the contrary, at 300 kGy, γ-irradiation produces the strongest modification of crystallinity and stacking order. Therefore, it provides a clear contrast compared to the pristine materials (GO and rGO). This allows direct demonstration of the irradiation impact. Also, other characterizations (e.g., Raman, FTIR, and XPS) were employed to follow the gradual chemical/structural changes at 50, 100, and 200 kGy. XRD was used specifically to confirm and highlight the end-point effect of irradiation on long-range ordering. Therefore, including all irradiation doses in the XRD plot would overcrowd the figure without adding significant new information, since the peak evolution is gradual. Showing only pristine and the most irradiated samples provides a clear, representative comparison without redundancy. 3.5. Water contact angle measurements Measurements of the water contact angle (CA) were conducted to assess the hydrophobic or hydrophilic properties of the prepared GO and rGO free-standing flexible films. Commonly, that the surfaces with contact angles ≥90◦are classified as hydrophobic, or water-repellent [30]. Table 3 represents the contact angle measurements for GO and rGO gamma-treated samples. The CA values are similar for GO and rGO in air across all doses. Slightly lower CA in rGO suggests marginally increased hydrophilicity—possibly due to surface restructuring or introduction of polar groups despite reduction. Gamma irradiation in an air atmosphere does not significantly alter surface wettability. GO shows greater changes in CA with increasing dose in IPA from 34◦to 63◦, indicating a shift from good hydrophilic to low hydrophobic behavior. This suggests that reduction is occurring (loss of oxygen-containing groups). rGO in IPA shows consistently higher CA values than to GO, indicating more hydrophobic character, which is expected for reduced materials. The decreasing trend in rGO CA from 54◦to 43◦may reflect surface oxidation or reorganization due to IPA-mediated irradiation. 3.6. EMI shielding measurements Fig. 6 shows the total shielding effectiveness plots for GO samples irradiated in air, IPA, and rGO irradiated in the same media, at all applied doses. EMI SE of GO_IPA_300 kGy sample could not be measured due to visible ruptures of the materials. Samples of GO air and GO IPA (Figуре 6 a, b) show a low EMI SE. A small improvement was noted after GO was irradiated in air at a dose of 200 kGy, from 0.31 dB to 0.52 dB, while irradiation in IPA resulted in a lowering of EMI SE to 0.09 dB. On the contrary, reduced free-standing GO irradiated air showed EMI SE above 20 dB, suggesting their excellent shielding performance. Samples irradiated with 50 kGy showed the highest values, along with the one irradiated at 300 kGy, while the lowest EMI SE was measured for the one irradiated at 200 kGy. In the case of rGO irradiated in IPA, doses of 50, 100, and 200 kGy showed similar effects on EMI SE, and all three samples showed a similar SE T (between 26 and 27 dB). In Fig. 7, the components of total shielding effectiveness, dissipation (L D ), and mismatch loss (L M ) are presented. In the case of GO gamma irradiated samples (Fig. 7a-d), the major portion of the total shielding effectiveness is due to L D , and with negligible L M , while in the case of rGO samples (Fig. 7e-h), both L D and L M are present; however, the L D component is the dominant one. The L M values in rGO gamma-irradiated samples are significantly higher than to L M in gamma-irradiated GO samples. These results indicated that the main mechanism of EMW attenuation is absorption, which is a characteristic trait of state-of-theart shielding materials. Results for GOp and rGOp (Fig. S6) showed average total shielding efficiency for GOp to be 0.36002±0.02458 dB (3.20294±0.27647 %), and 18.69275±0.77286 dB (88.23828±1.01234 %) for rGO. By comparing the EMI SE of all samples, it is noticed that the higher applied dosages of gamma irradiation contribute higher to the EMI SE of GO irradiated in air, while irradiation in IPA improves EMI SE at lower applied dosages (50 and 100 kGy) (Fig. 8a, b). In the case of rGO samples, a slight improvement in EMI SE was observed after gamma irradiation at 300 kGy (Fig. 8c), 95.5 %, compared to 94.5 to 94.8 % calculated for other dosages. Although the SE T values slightly increased at 300 kGy, these results showed a surprising effect on EMI SE, considering that high-dose gamma irradiation induces defect formation in graphene-based nanomaterials [21,24], it was expected that gamma irradiation might affect the negative EMI shielding performances of GO materials. These results could be explained by the formation of cross-layer bridges between graphene sheets, as previously observed at nanotubes and the creation of an additional path for signal attenuation. EMI SE of GO and rGO is markedly affected by their oxidation degree, defect density, and electrical conductivity. GO is extensively oxidised, featuring a variety of oxygenated functional groups (e.g., hydroxyl, epoxy, carboxyl) that interfere with the π -conjugated network. These groups diminish electrical conductivity, rendering GO an ineffective EMI shield unless combined with conductive additives or utilised in multilayer composites. However, oxygen groups facilitate interfacial polarisation, which may lead to dielectric loss and absorption-type shielding. In rGO, moderate defect levels can improve EMI shielding by amplifying multiple scattering and reflection of electromagnetic waves, as well as enhancing polarisation centres for dielectric loss. Excessive flaws can impair conductivity and diminish reflectiondominated shielding. Electrical conductivity is the main feature for reflection-dominated electromagnetic interference shielding. rGO, particularly when adequately reduced through thermal or chemical methods, reinstates sp² carbon networks, therefore markedly enhancing conductivity. Increased conductivity results in enhanced reflection of electromagnetic waves and improved shielding efficiency, especially within the higher-frequency microwave spectrum. Gamma irradiation can promote wrinkling or folding of rGO sheets due to radiolysisinduced strain, which increases surface roughness, multiple reflection pathways, and traps and attenuates EM waves more effectively [8,20,35, 42,53]. Compared to non-irradiated samples (GO and rGO), gamma irradiation improved the EMI SE of free-standing films irradiated in the air and IPA at all applied doses. The effects of applied doses on EMI SE are not significant. Improvement of EMI SE free-standing GO and rGO by gamma irradiation is associated with two main effects of gamma rays towards graphene sheets: •creating cross-layer bridges between the sheets and O-functional groups, removing by irradiation in IPA, it ensured charge traveling across the layer and charge hopping from one sheet to another, enhancing the conduction loss [4]; Table 3 CA measurements for GO and rGO gamma-ray-treated samples. Sample CA (◦) Sample CA (◦) GOp 61 rGOp 38 GO_air_50kGy 48 rGO_air_50kGy 44 GO_air_100kGy 49 rGO_air_100kGy 47 GO_air_200kGy 46 rGO_air_200kGy 46 GO_air_300kGy 46 rGO_air_300kGy 44 GO_IPA_50kGy 34 rGO_IPA_50kGy 54 GO_IPA_100kGy 53 rGO_IPA_100kGy 49 GO_IPA_200kGy 63 rGO_IPA_200kGy 45 GO_IPA_300kGy 55 rGO_IPA_300kGy 43 J.P. Filipovic et al. Chemical Engineering Journal Advances 24 (2025) 100873 9