Revealing enhanced X-Ray radiation shielding of 2D layered materials and their laminar heterostructures

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Nine, Tran T. Tung, Ana C. Pereira, Kamrul Hassan, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3076104/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 13 Oct, 2023 Read the published version in Graphene and 2D Materials → Version 1 posted 7 You are reading this latest preprint version Abstract This paper demonstrates a new concept of using two-dimensional (2D) layered materials and their heterostructures for enhanced X-ray radiation shielding. This phenomenon is revealed by characterization the X-ray shielding performances of several 2D materials with high atomic numbers (Z) including MoS 2 , antimonene (Sb), and MXene prepared as multi-layered and heterostructured films by assembly of their few-layer (FL) sheets. Results showed considerable X-ray shielding enhancement of (40-50 %) at 30kVp for individual 2D multi-layered films compared with their bulk structures of these materials. Furthermore, when these multi-layered films were combined into laminar heterostructures structures (e.g. MoS 2 +MXene) further enhancement of ca 60 % was achieved. The mechanism of the observed X-ray shielding enhancement by these multi-layered 2D structures is not clear at this stage. It is postulated to be the result of an additional multiple scattering and reflections of photons between multiple layers of 2D crystals inside the film, that is not occurred in uniform bulk material. The presented results suggest that multi-layered 2D materials with high atomic numbers (Z) and their laminar heterostructures can offer a new and promising strategy for designing of a new generation of Pb-free radiation-shielding materials that is urgently needed across broad sectors. 2D materials multi-layered structure heterostructures X-rays shielding Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1 Introduction There is a growing demand for improving protection from exposed ionising radiations such as X-rays used across broad sectors including medical, mining, nuclear, military and space industry [1]. To protect operators from overexposure to hazardous X-rays, an efficient, low-cost, affordable, and efficient radiation shielding materials are needed [2]. Medical irradiation used in diagnostics is considered as one of the largest artificial sources of radiation exposure, which is of great concern to human health [1–2]. Protective metallic lead (Pb) in different forms such as foils, plates, bricks, glass, and Pb-based garments is conventionally used for X-ray protection able to block and absorb most of this radiation [1, 3–6]. However, Pb-based materials have many disadvantages, such as being extremely heavy, uncomfortable to wear, toxic, non-disposable, and environmentally unsustainable [6–7]. To develop a new generation of lightweight, non-toxic, and sustainable Pb-free radiation shielding materials that comply with the international standards for X-ray radiation protection, is significant for many sectors. To achieve these goals, several materials with high atomic numbers (Z) and densities, such as tin (Sn), antimonene (Sb), tungsten (W), and bismuth (Bi) and their combination have been explored as potential Pb alternatives [8–11]. Most of these materials were prepared in the forms of polymer-based composites, but also as the films, and fabrics showing promising shielding performances [12–13]. Although polymer-based composites have been widely used for the formation of lightweight Pb-free X-ray shielding materials, the pinholes and voids within the composites have a negative effect on X-ray attenuation, as the incident X-rays can easily pass through these voids [8]. To address this issue, the use of materials with a densely packed structures in the film forms is shown to be more desirable and able to reduce the penetration of incident X-rays. To improve the performance of x-ray shielding films studies from several groups and ours have shown that using metal oxide forms with high atomic numbers (Z) with nano scale dimensions with high surface-to-volume (SA/V) ratios can provide improved shielding performance [14–16]. This is because the high SA/V nanomaterials are homogenously dispersed in the film to create a densely packed layer. These results also indicate that by designing the internal architecture of the material, it is possible to further enhance their radiation-shielding performance compared to their uniform bulk structures. Since the debut of graphene in 2004, the 2D materials have received their designation as “materials of the 21st century” owing to their unique monoatomic 2D structures and outstanding properties, including physical, chemical, electrical, optical, magnetic, thermal, mechanical etc [17]. They have opened new horizons in materials science and engineering to create novel materials, properties, and devices for a broad range of applications [18]. It was recently discovered that the combination of two or more 2D materials in the form of laminated structures could generate new and more intriguing properties, which are different from their single-layer structures [19–20]. This opens unprecedented opportunities for new discoveries and applications using 2D layered structures [21–22]. Following these studies, it is reasonable to expect that layered and laminated structures of 2D materials may have different effects on the radiation-shielding properties across broad electromagnetic range that is demonstrated in several studies [23–25]. Study by Vogl et al showed gamma-radiation tolerance of 2D materials such as hBN and MoS 2 indicating their potential to be used for the device protection in space explorations [24]. The applications of 2D layered materials such as graphene and MXene was reported for electromagnetic interference shielding (EMI) owing to their unique layered structure [25–28]. First study showing that laminated 2D antimonene (Sb) has an efficient shielding against X-ray radiation is recently presented by our group indicating the probability of X-ray scattering and interaction, leading to an enhanced X-ray shielding ability [29]. Inspired by these studies this paper present experimental demonstration of new concept that multi-layered and laminar heterostructures of 2D materials can significantly enhance X-ray shielding. This phenomenon is illustrated in Fig. 1 showing SEM image and schematic of 2D multi-layered structure with proposed interactions of x-rays with these structures compared with bulk material. The X-ray shielding by these 2D structure is explained to be a result of the multiple scattering and interactions (scattering) of the photons occurring at the top and interface between each layer in multi-layered structure causing significant shielding results that is not observed in the bulk structures. Considering the unique structural properties of 2D materials organized in the films by the self-assembly of their 2D crystal sheets into multiple layers, each layer could act as a shielding barrier reducing photon energy by multiple internal scattering and absorption. We believe this shielding concept is universal and can be applied for shielding other ionizing radiation (gamma-rays, neutron). To demonstrate this X-ray shielding concept by 2D multi-layered, we prepared these films using several different 2D materials with high atomic Z numbers, such as MoS 2 , antimonene (Sb), and MXene. The films were made by self-assembly of their nanosheets with few atomic layers prepared by a common exfoliation process. In addition, laminar heterostructures were created by combining two or more individual multi-layered films, such as MoS 2 + MXene to explore their impact on shielding properties. The X-ray shielding performance at low- energy X-rays (30 kVp) was investigated for all prepared films (experimental set-up Figure S1 ) and compared with that of their complementary films composed of bulk structures using the same mass. 2 Experimental 2.1 Chemicals and materials : Molybdenum disulfide powder (MoS2, 99.99%, 23 µm) and sodium bromide (NaBr) was purchased from Chem-Supply (Australia). Bulk crystalline antimonene (Sb) with 99.9% purity was purchased from Smart Elements, Austria. The Ti 3 AlC 2 MAX was supplied by Carbon-Ukraine. Carboxymethylcellulose sodium salt (CMC, high viscosity) and isopropanol (reagent grade, ≥ 99.5%) was provided by Sigma-Aldrich (Australia). 2.2 Preparation of 2D materials : Bulk MoS 2 powder was exfoliated into single layer MoS 2 sheets using a Planetary Ball Mill PM 200 (Retsch, Australia) with zirconium balls (3 mm in diameter)3 [30]. NaBr was added to facilitate the process of the ball milling with a weight ratio of NaBr: MoS 2 at 20:1, and the weight ratio of balls to powder was also 20:1. After the dry ball milling process, NaBr in the as-prepared mixture was removed by washing several times using distilled (DI) water with the aid of a centrifuge (Sigma, Australia, 4200rpm) and then dried in oven at 50℃ overnight for the further step. The synthesis steps of 2D MXene nanosheets was performed followed a literature guideline [23,28,31] Briefly, the small pieces of Ti 3 AlC 2 MAX phase were ground into fine powders using a mortar, and the powders having a particle size of less than 25 µm were selected by a 25 µm sieve and collected for further use. Lithium fluoride (1.5 g) was added to 20 ml of 9M HCl solution in a reaction vessel under and stirred with a magnetic bar, then 1 gram of Ti 3 AlC 2 was slowly added into the solution. The mixture was maintained in an oil bath environment at 35 ºC for 24 h. After the etching reaction was completed, the reacted mixture was subjected to centrifugal washing with deionized H2O at 3500 rpm for 30 minutes. This washing procedure was repeated 5 to 6 times until the pH value reached around 6, and a relatively pure Ti 3 AlC 2 x product (MXene) was obtained. After washing, the product was ultrasonically separated to obtain a two-dimensional layered MXene material. A small amount of MXene powder was obtained by drying the raw MXene material, and its electrical conductivity was tested. Few-layer antimonene (FL-Sb) nanosheets were prepared in a 4:1 isopropanol/water mixture by exfoliating bulk Sb crystals using a combination of ball milling and ultrasonication [29]. Bulk Sb crystals were put in a zirconia milling pot with isopropanol/water solvent. The samples were then ball-milled using Retsch planetary ball mill (PM 200) with zirconia balls (1 mm) at 300 rpm for 30 min. After drying, the ball-milled Sb flakes (30 mg) were re-dispersed in 4:1 isopropanol/water mixture (10 mL) for further exfoliation. The exfoliation was carried out in a bath ultrasonication for 40 min. Then the resulting black suspension was centrifuged at 3000 rpm for 3 min, and the dark grey supernatant was recovered. 2.3 Preparation of 2D multi-layered films and their laminar heterostructures : Few-layer exfoliated MoS 2 were dispersed with DI water and then bath-sonicated for 1 h, respectively. CMC solution (0.5 wt.%) was added to the as-prepared MoS 2 solution with the optimized weight ratio to prepare dispersion with known MoS2 concentration of 10 mg/ml. The mixture was then stirred constantly for 3 h at the room temperature (20 ± 2 ℃) followed by composed of multi-layered structures of assembled MoS 2 sheets. The prepared MoS 2 film was then dried for 12 h in air at the room environment (20 ± 2 ℃) and used as a freestanding film for X-ray experiments. The mass loading and thickness of the film was measured to be consistent with prepared films using other 2D materials. The MXene films were produced by the same method of vacuum filtration as following details using MXene dispersion in deionized water that was sonicated for 1 hour before filtration. Required volumes (2 ml to 8 mL) of as-prepared MXene solutions were slowly filtrated by a vacuum filtration system to form MXene layered films on the membranes. The MXene-deposited membrane connected to the suction filter was placed in a vacuum drying oven and dried at 40ºC for 12 h. After that, the entire system was taken out from the vacuum drying oven, the suction filter was removed, and then the dried MXene film was carefully separated from the membrane and used for X-ray measurements. Similar process was applied to make 2D antimonene multi-layered films using prepared 2D FL-Sb dispersion with known concentration and volume to achieve with the same mass loading as 2D MoS 2 and 2D MXene films. Double laminar heterostructure films were prepared by stacking individual 2D MoS 2 layered film and individual 2D MXene layered film into one combined structure (MoS 2 /MXene). Quadrupole laminar heterostructure films were prepared by double stacking individual 2D MoS 2 layered films and individual 2D MXene layered films into the combined structure (MoS 2 /MXene/ MoS 2 /MXene). 2.4 Characterizations : A scanning electron microscope (SEM-FEI Quanta 450, Japan) in a low vacuum chamber at an accelerating voltage of 5 kV. The average thickness and particle topography of exfoliated FL-Sb was examined using an NT-MDT Ntegra Solaris Atomic Force Microscope (AFM) via tapping mode. NT-MDT SPM Software (Nova 1.0.26) was used for AFM image processing. A particle size analyzer from Malvern instrument (NanoSight NS300) was used to examine the average particle size distribution. A transmission electron microscope (TEM, FEI Titan Themis) was used to acquire nanoscale morphology and elemental analysis of exfoliated substances. Thermogravimetric analysis (TGA) of FL-Sb, PDMS and their composite were studied using Mettler-Toledo TGA/DSC 2, Switzerland in an air atmosphere at a constant heating rate of 5°C/min. The vibrational stretching modes of different molecular bonds in PDMS modified samples were studied by Fourier transform infrared spectroscopy (FTIR) (Nicolet 6700 Thermo Fisher, USA). 2.5 X-ray radiation measurements : X-ray transmission testing was performed using a superficial X-ray tube (SXR) unit (Gulmay D3150, UK) as shown in Figure S7. The distances between the X-ray tube and sample-placing panel and sample-placing panel to the detector were equally 50 cm. The samples were exposed to the X-ray voltage range at 30, 50, 80, 100 kVp, respectively, for 0.50 min with the X-ray transmitted sample placing area of diameter at 1 cm, and the X-ray attenuation performance was evaluated as the transmission dose of samples divided by the transmission dose without the sample. Each sample was measured 3 times and determined by the arithmetic mean. The X-ray attenuation of an X-ray beam is expressed as a function of the linear attenuation coefficient (µ) and calculated using equation and procedure as reported elsewhere. 3 Results and discussion 3.1 Fabrication and characterization of prepared multi-layered structures of 2D materials Comprehensive physical, chemical and thermal characterization of the synthesized few-layers MoS 2 sheets, antimonene and MXene and their layered films are summarized in Fig. 2 and Figure S2-S4. A ball-milling method was employed to exfoliate a large quantity of micron sized MoS 2 sheets with an average particle size of 22 µm ( Figure S2 ) into few-layers nanosheets with an average particle size of 432 nm (Fig. 2 a and Figure S2 ). The corresponding SEM and TEM image ( Figure S2 (a) and Fig. 2 a) confirmed the presence of the sheet-like MoS 2 structure with significant changes in their particle size and morphology. High-resolution TEM images showed exfoliated MoS 2 nanosheet with ~ 7 layers (inset of Fig. 2 a. Raman, XRD, and FTIR analyses ( Figure S2 ) confirmed their significant differences from that of bulk MoS 2 . Few-layers MXene was prepared using a common etching process from Ti 3 AlC 2 MAX phase materials as described in the literature [25–26]. Their typical structure characterized by SEM and TEM is presented in Fig. 2 b and Figure S2 confirms a few-layer structure of MXene with the dimension of a few hundred nanometers. Few-layer 2D antimonene (FL-Sb) nanosheets were synthesized in a 4:1 isopropanol/water mixture by exfoliating bulk Sb crystals using a combination of ball milling and ultrasonication, and the structural differences before and after exfoliation are summarized in Fig. 2 c and Figure S3. The exfoliation of bulk-Sb (30–45 µm, Figure S3a transforms it into nanosheets (confirmed by TEM in Fig. 2 c and Figure S3c ) with an average lateral dimension ranging between 300–400 nm (confirmed by particle size distribution Figure S3d ). Figure S3e presents the powder diffraction pattern of exfoliated FL-Sb nanosheets showing typical signature of Sb nanopowder, which is in good agreement with the standard diffraction card “JCPDS no. 01-085-1324”. These 2D sheet structures dispersed in solution, were used to fabricate their multi-layered films by a vacuum filtration process. During this process 2D sheets were self-assembled into a layered film structure and their typical cross-section SEM images are presented in Fig. 2 d-f. These images clearly confirm the formation of their layered film structure composed of thousands of layers assembled 2D sheets that is supposed have a strong Van Der Waals interaction between layers. It is worth nothing that these layered films can be prepared with the controllable thickness from tens to several hundreds of microns including making their heterostructure films by combining different 2D materials. 3.2 X-Ray shielding performance of multi-layered structures of 2D materials The study on X-ray transmission and the attenuation enhancement of the prepared individual 2D MoS 2 , MXene and antimonone layered films compared to their corresponding bulk films are presented in Fig. 3 and Table S1 . These results showed a significant decrease in the X-ray transmission of the 2D layered films at 30 kVp, compared to their bulk counterparts. Figure 3 b confirmed that the X-ray attenuation enhancement rate of 46.67% for MoS2 film, 37.28% for 2D antimonene enhancement rate of 46.67% for MoS 2 film, 37.28% for 2D antimonone film and 41.07% for MXene film is achieved compared to their bulk films. It is worth noting that the mass loading of all the prepared films including controls had a similar mass (g/m 2 ), to make the observed results related only to differences in mass or density. The results obtained at a lower X-ray energy of 30 kVp are presented where the X-ray attenuation enhancement difference is the most significant and relevant. However, the X-ray transmission measurements at the higher energy of 50 kVp and 80 kVp were also performed showing the same trend, but with lower shielding enhancement (data not shown) indicating this phenomenon is more prominent at lover energies. To improve the shielding performance at higher energies a combination with other materials should be considered. It is well known that that X-ray shielding is dependent on the thickness of the material and by increasing the thickness of these 2D multi-layered films, it will be possible to further improve their performances. This optimization was further demonstrated by controlling the film thickness in case of MoS 2 layered films prepared with different thickness or masses per surface area. Figure S5 presents the X-ray transmission results showing that by increasing their thickness of the MoS 2 films from 0.11 mm to 1.34 mm this could effectively attenuate the X-ray transmission down to 0.09%. The X-ray transmission value of the exfoliated MoS 2 film with the optimized thickness of 1.34 mm was further evaluated compared with 0.20 mm Pb sheet indicating comparable performance to 0.20 mm Pb-equivalent attenuation at 30 kVp (inset of Figure S5 ). Although the optimized thickness (1.34 mm) of layered 2D MoS 2 film was much thicker than the 0.20 mm Pb sheet, the weight of this film (minus the holding substrate) at 1.18 g was 50% lighter than the 0.20 mm Pb (2.17 g). This can be defined as outstanding results and comparable to Pb benchmark materials indicating layered 2D materials as very promising solution for the development of new generation of lightweight and Pb-free shielding materials for broad protection applications. 3.3 X-Ray shielding performance of multi-layered and laminar heterostructures In the following experiment the X-ray radiation shielding performance of the films with multi-layered and laminar heterostructure of 2D materials prepared by combining two or more individual multi-layered films such as MoS 2 and MXene was explored. One combination of these double laminar multi-layered films was made using the MoS 2 film on the top and the MXene film on the bottom (MoS 2 /MXene). The second was composed by the MoS2 and MXene films subsequently ordered as quadruple laminar heteostructures (MoS 2 /MXene/MoS 2 /MXene). Comparison of obtained X-ray transmission results on these films are presented in Fig. 4 . The results showed that the double laminar heterostructures have increased X-ray shielding enhancement to their individual multi-layered for 12.85% MoS 2 and 6.62% MXene with the same mass loading. However, the films with quadruple laminar heterostructure multi-layered films showed further significant shielding of 62.26% for MoS 2 and 59.57% for MXene compared to their films composed with individual multi-layers. By changing the orientation of these laminates such MXene at the top/ MoS 2 on bottom or reverse no difference was observed. These results suggest possible synergetic effect with increasing number of laminates from 2 to 4 that was surprising, that is possibly, caused by an additional scattering of X-rays at the interface between these laminated structures. However, more studies are needed to understand the mechanism of these enhancements by heterostructures. These results suggests that by increasing number of laminates of the 2D multi-layered films we could further enhance shielding performance. This is another promising strategy to further improve the X-ray shielding performance, which deserves to be explored in the future with studies and details. These presented results clearly reveal experimental evidence that multi-layered 2D materials and their laminar heterostructures can enhanced X-ray shielding showing new properties not observed before. To provide theoretical validation of this experimental evidence we try to perform the Monte Carlo simulation used for modelling of X-ray attenuation of bulk materials. However, our attempt to perform theoretical simulation by the Monte Carlo simulation to predict these properties was not very successful. Main reason was because of the high complexity of the model to describe the multi-layered and laminar heterostructures of 2D materials used in our study. So far, conventional physical models consider uniform bulk structure where shielding is dependent of parameters such as Z atomic number, density and the film thickness and there has been no simulation model for the interaction with multi-layered 2D structures. The complexity of this model is related to consideration of many parameters such as the size and morphology of individual 2D crystal sheets, number of their atomic layers, their crystallinity, number and layers in the film, their interlayer distances, Van Der Waals interactions between layers, the interfaces between laminated structures, number of laminates etc. The interaction of X-ray photons inside these multi-layered structures because of these parameters is reasonable to be different from that of the bulk structure of material. We expect these models will be developed in the future enabling to theoretically verify the experimental results presented in this paper and predict how to improve designing more optimized heterostructures and their combinations. The X-ray attenuation is known as the process of the X-ray intensity reduction via either absorption or scattering when X-ray photons pass through the shielding material [1–2]. It involves three interaction mechanisms including (1) photoelectric effect, (2) Compton scattering, and (3) pair production [27]. To explain the observed attenuation results of the 2D layered materials, we assumed that the X-ray shielding performance could be enhanced because of multiple scattering and absorption occurring during the incoming X-ray photons that interacted with these layered films. This type of scattering process is less relevant within the bulk materials, where most of the deflection occurred on the top surface, as schematically presented in Fig. 1 . The multi-layered 2D material films can increase the probability of photoelectric effect within each layer, inside the films leading to enhanced X-ray shielding ability. In other words, incident X-ray is absorbed and reflected many times between each layer (+ 1000 layers) within the layered 2D material films which makes their attenuation properties much higher compared to non-layered and bulk materials. In terms of the combination of two or more 2D layered films and their heterolaminar structures, the multiple interfaces between each layer of the 2D laminates will provide additional scattering and absorption of X-ray photons multiple times as shown in Fig. 5 . This is reasonable explanation for observed shielding enhancement, but more studies are needed to fully reveal the mechanism of X-ray interactions within these 2D layered heterostructures in addition to establishing their appropriate models to describe and predict these interactions for range of 2D materials with high Z number. Conclusions In summary, the presented study practically demonstrates that the multi-layered films composed of 2D materials such as MoS 2 , MXene and antimonene and their laminar heterostructures can significantly attenuate low energy (30 kVp) X-ray rays. The phenomenon is explained as results of multiple scattering and absorption inside the 2D multi-layered film structures that is not occurred in bulk material. The X-ray shielding enhancement of 46.67% for layered MoS 2 , 37.28% for antimonene and 41.07% for MXene, was determined compared with their bulk counterparts. Further and surprising enhancement of X-ray shielding was achieved by combination of individual films such as MoS 2 and MXene to create heterostructure (double and quadruple laminates) showing 62.26% and 59.57% compared to their individual MoS 2 and MXene layered films. This paper presents exciting discovery about X-ray shielding properties of 2D materials and their heterostructures not considered before that will open a new horizon for designing a new Pb-free radiation shielding technology and their successful application across broad sectors in medicine, nuclear industry, space exploration, and defence. Further studies on the theoretical modelling on photon interactions with 2D multi-layered structures are needed to give more insights to understand this mechanism and help development of more advanced shielding structures. Declarations Supplementary Information: The online version contains supplementary material presenting characterization results prepared 2D materials including TEM, SEM, EDAX, particle size. XRD, Raman spectroscopy measurements) is available at XXX There are no conflicts to declare. Acknowledgements The authors acknowledge the financial support from the ARC Research Hub for Graphene Enabled Industry Transformation, (IH150100003). We thank Australian Microscopy for the access of SEM, TEM facilities, Mr. Ken Neubauer, Dr. Ashley Slattery for their technical support on SEM and TEM measurements. References E.B. Podgorsak, Radiation Physics for Medical Physicists, 2016, Springer Berlin, Heidelberg M.E Noz, G.Q.Maguire, Radiation protection in health sciences. 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Supplementary Files GA.png Graphical abstract Supportinginformation2023.docx Cite Share Download PDF Status: Published Journal Publication published 13 Oct, 2023 Read the published version in Graphene and 2D Materials → Version 1 posted Editorial decision: Major revision 05 Jul, 2023 Reviews received at journal 24 Jun, 2023 Reviewers agreed at journal 19 Jun, 2023 Reviewers invited by journal 19 Jun, 2023 Editor assigned by journal 19 Jun, 2023 Submission checks completed at journal 19 Jun, 2023 First submitted to journal 17 Jun, 2023 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3076104","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":211236350,"identity":"56fa0286-2b31-46d6-ba65-b4032cb6c447","order_by":0,"name":"Le Yu","email":"","orcid":"","institution":"University of Adelaide","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Le","middleName":"","lastName":"Yu","suffix":""},{"id":211236351,"identity":"ea1ea256-5047-44f1-8f84-6303aef65c4d","order_by":1,"name":"Md J. Nine","email":"","orcid":"","institution":"University of Adelaide","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Md","middleName":"J.","lastName":"Nine","suffix":""},{"id":211236352,"identity":"f91a8e61-3f33-4f4a-8de5-7b5521e44045","order_by":2,"name":"Tran T. Tung","email":"","orcid":"","institution":"University of Adelaide","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Tran","middleName":"T.","lastName":"Tung","suffix":""},{"id":211236353,"identity":"79a95871-0c26-4407-8a9c-01828aab5f6e","order_by":3,"name":"Ana C. Pereira","email":"","orcid":"","institution":"University of Adelaide","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ana","middleName":"C.","lastName":"Pereira","suffix":""},{"id":211236356,"identity":"9f09dae2-1b8b-4814-b00c-38aa295628ed","order_by":4,"name":"Kamrul Hassan","email":"","orcid":"","institution":"University of Adelaide","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Kamrul","middleName":"","lastName":"Hassan","suffix":""},{"id":211236358,"identity":"791aac80-3252-41f9-843e-8977ffce2b2c","order_by":5,"name":"Diana Tran","email":"","orcid":"","institution":"University of Adelaide","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Diana","middleName":"","lastName":"Tran","suffix":""},{"id":211236359,"identity":"d682774d-8a03-49b2-b993-9eb570924e5d","order_by":6,"name":"Alexandre Santos","email":"","orcid":"","institution":"University of Adelaide","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Alexandre","middleName":"","lastName":"Santos","suffix":""},{"id":211236360,"identity":"e7cb96e1-13d4-47a6-aba4-02e26bdc914d","order_by":7,"name":"Dusan Losic","email":"data:image/png;base64,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","orcid":"","institution":"University of Adelaide","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Dusan","middleName":"","lastName":"Losic","suffix":""}],"badges":[],"createdAt":"2023-06-17 13:59:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3076104/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3076104/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s41127-023-00064-4","type":"published","date":"2023-10-13T15:01:58+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":39114437,"identity":"933fa372-7f0b-4ef8-a041-b00f273363be","added_by":"auto","created_at":"2023-06-26 19:12:00","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":423299,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Cross-sectional SEM images showing typical 2D structure of the film created by self-assembly of 2D nanosheets, which are schematically presented on the right. (b) Schematic illustration of the interaction between X-ray photons and the multi-layered structure of 2D crystals, showing multiple scattering occurred between each layer causing significant X-ray shielding that is not occurred in bulk material. The enhancement of X-ray attenuation by 2D multi-layered is presented on the right graph showing comparison with corresponding bulk material with the same thickness (or mass of material)\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3076104/v1/6579480ec566e9f8bdb4a48b.png"},{"id":39113292,"identity":"36ab55ee-cb78-452d-86ee-81b1c7125a4a","added_by":"auto","created_at":"2023-06-26 19:04:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":758299,"visible":true,"origin":"","legend":"\u003cp\u003ea) SEM and TEM images of the exfoliated nanosheets from the selected 2D materials a) SEM images of 2D MoS\u003csub\u003e2 \u003c/sub\u003enanoplatelets (scale bar = 1 μm) b) TEM images of 2D MXene nanosheets showing their few layers structure (inset), c) TEM images of 2D antimonene (Scale bar = 100 nm) with inset confirming few layers structure. Cross-sectional SEM images of the prepared films confirming their multi-layered structure d) MoS\u003csub\u003e2\u003c/sub\u003e, e) MXene (scale bar = 50 μm)\u0026nbsp; and f) antimonene (scale bar = 50 μm)\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3076104/v1/213f5494250875e7f3df62da.png"},{"id":39113296,"identity":"c4126636-bf92-42d5-8992-e2485b19eee4","added_by":"auto","created_at":"2023-06-26 19:04:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":248750,"visible":true,"origin":"","legend":"\u003cp\u003eComparative X-ray transmission results performed at 30 kVp showing a) difference in X-ray shielding performance between multi-layered films of selected 2D materials composed of self-assembled 2D sheets of MoS\u003csub\u003e2\u003c/sub\u003e, antimonene and MXene and their control bulk structures; b) the X-ray attenuation enhancement rate in % of layered 2D films compared to their bulk films. All tested materials were used with the same mass loading in the film and measurements performed in triplicate.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3076104/v1/0733b359229342e4f193255e.png"},{"id":39113293,"identity":"37637635-67cd-4cd1-aac7-7384e1658b2d","added_by":"auto","created_at":"2023-06-26 19:04:00","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":324826,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray transmission results performed using 2D multi-layered materials and their laminar heterostructures combined by MoS\u003csub\u003e2\u003c/sub\u003e and MXene in the forms of double (MoS2/MXene) and quadruple (MoS2/MXene/MoS2/MXene) films; b) the enhancement rate of multi-layered laminar heterostructures compared to individual 2D MoS\u003csub\u003e2\u003c/sub\u003e layered film, and c) the enhancement rate of multi-layered heterostructures compared to individual 2D MXene layered film. All tested materials were used with the same mass loading and a X-ray shielding experiment was performed at 30 kVp and measurements in triplicate.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3076104/v1/f9d85afe7c2833003069e4c3.png"},{"id":39114436,"identity":"d811b763-b1a0-4689-83ed-4e4ca467e331","added_by":"auto","created_at":"2023-06-26 19:12:00","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":545120,"visible":true,"origin":"","legend":"\u003cp\u003eThe schematic illustration to explain a significant enhancement of X-ray attenuation or reduction of x-ray transmission (It) on individual 2D multtlayered materials (ml) and their heterolaminar structures (ml+hl) with corresponding bulk structure. This enhancement is presented as results of increased internal scattering of photons inside 2D layers which significantly reduce their transmission through the structure compared to uniform bulk material. The % of X-ray attenuation caused by scattering between each layer inside multi-layered film (ml) composed on of individual 2D material (1) is further enhanced by additional scattering at the interface (I) when the film is composed with the heterloaimnar architecture with two 2D(2) layered materials (mL).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3076104/v1/37da200548820fe430650517.png"},{"id":44699982,"identity":"10af22cb-19dd-43eb-978d-023c7c496352","added_by":"auto","created_at":"2023-10-16 15:09:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2407042,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3076104/v1/89c7f5dc-9127-486a-ae77-3c284d0e7a02.pdf"},{"id":39113298,"identity":"b11035d1-5bd9-48e8-9789-76602e303ac7","added_by":"auto","created_at":"2023-06-26 19:04:00","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":279751,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical abstract\u003c/p\u003e","description":"","filename":"GA.png","url":"https://assets-eu.researchsquare.com/files/rs-3076104/v1/26741eca3a1feb43e3245230.png"},{"id":39113294,"identity":"c72c1d79-08d8-4564-bc62-0c2e14997462","added_by":"auto","created_at":"2023-06-26 19:04:00","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":2177183,"visible":true,"origin":"","legend":"","description":"","filename":"Supportinginformation2023.docx","url":"https://assets-eu.researchsquare.com/files/rs-3076104/v1/71fa1d6289492d93706680b8.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Revealing enhanced X-Ray radiation shielding of 2D layered materials and their laminar heterostructures","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThere is a growing demand for improving protection from exposed ionising radiations such as X-rays used across broad sectors including medical, mining, nuclear, military and space industry [1]. To protect operators from overexposure to hazardous X-rays, an efficient, low-cost, affordable, and efficient radiation shielding materials are needed [2]. Medical irradiation used in diagnostics is considered as one of the largest artificial sources of radiation exposure, which is of great concern to human health [1\u0026ndash;2]. Protective metallic lead (Pb) in different forms such as foils, plates, bricks, glass, and Pb-based garments is conventionally used for X-ray protection able to block and absorb most of this radiation [1, 3\u0026ndash;6]. However, Pb-based materials have many disadvantages, such as being extremely heavy, uncomfortable to wear, toxic, non-disposable, and environmentally unsustainable [6\u0026ndash;7]. To develop a new generation of lightweight, non-toxic, and sustainable Pb-free radiation shielding materials that comply with the international standards for X-ray radiation protection, is significant for many sectors.\u003c/p\u003e \u003cp\u003eTo achieve these goals, several materials with high atomic numbers (Z) and densities, such as tin (Sn), antimonene (Sb), tungsten (W), and bismuth (Bi) and their combination have been explored as potential Pb alternatives [8\u0026ndash;11]. Most of these materials were prepared in the forms of polymer-based composites, but also as the films, and fabrics showing promising shielding performances [12\u0026ndash;13]. Although polymer-based composites have been widely used for the formation of lightweight Pb-free X-ray shielding materials, the pinholes and voids within the composites have a negative effect on X-ray attenuation, as the incident X-rays can easily pass through these voids [8]. To address this issue, the use of materials with a densely packed structures in the film forms is shown to be more desirable and able to reduce the penetration of incident X-rays. To improve the performance of x-ray shielding films studies from several groups and ours have shown that using metal oxide forms with high atomic numbers (Z) with nano scale dimensions with high surface-to-volume (SA/V) ratios can provide improved shielding performance [14\u0026ndash;16]. This is because the high SA/V nanomaterials are homogenously dispersed in the film to create a densely packed layer. These results also indicate that by designing the internal architecture of the material, it is possible to further enhance their radiation-shielding performance compared to their uniform bulk structures.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSince the debut of graphene in 2004, the 2D materials have received their designation as \u0026ldquo;materials of the 21st century\u0026rdquo; owing to their unique monoatomic 2D structures and outstanding properties, including physical, chemical, electrical, optical, magnetic, thermal, mechanical etc [17]. They have opened new horizons in materials science and engineering to create novel materials, properties, and devices for a broad range of applications [18]. It was recently discovered that the combination of two or more 2D materials in the form of laminated structures could generate new and more intriguing properties, which are different from their single-layer structures [19\u0026ndash;20]. This opens unprecedented opportunities for new discoveries and applications using 2D layered structures [21\u0026ndash;22]. Following these studies, it is reasonable to expect that layered and laminated structures of 2D materials may have different effects on the radiation-shielding properties across broad electromagnetic range that is demonstrated in several studies [23\u0026ndash;25]. Study by Vogl et al showed gamma-radiation tolerance of 2D materials such as hBN and MoS\u003csub\u003e2\u003c/sub\u003e indicating their potential to be used for the device protection in space explorations [24]. The applications of 2D layered materials such as graphene and MXene was reported for electromagnetic interference shielding (EMI) owing to their unique layered structure [25\u0026ndash;28]. First study showing that laminated 2D antimonene (Sb) has an efficient shielding against X-ray radiation is recently presented by our group indicating the probability of X-ray scattering and interaction, leading to an enhanced X-ray shielding ability [29].\u003c/p\u003e \u003cp\u003eInspired by these studies this paper present experimental demonstration of new concept that multi-layered and laminar heterostructures of 2D materials can significantly enhance X-ray shielding. This phenomenon is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e showing SEM image and schematic of 2D multi-layered structure with proposed interactions of x-rays with these structures compared with bulk material. The X-ray shielding by these 2D structure is explained to be a result of the multiple scattering and interactions (scattering) of the photons occurring at the top and interface between each layer in multi-layered structure causing significant shielding results that is not observed in the bulk structures. Considering the unique structural properties of 2D materials organized in the films by the self-assembly of their 2D crystal sheets into multiple layers, each layer could act as a shielding barrier reducing photon energy by multiple internal scattering and absorption. We believe this shielding concept is universal and can be applied for shielding other ionizing radiation (gamma-rays, neutron). To demonstrate this X-ray shielding concept by 2D multi-layered, we prepared these films using several different 2D materials with high atomic Z numbers, such as MoS\u003csub\u003e2\u003c/sub\u003e, antimonene (Sb), and MXene. The films were made by self-assembly of their nanosheets with few atomic layers prepared by a common exfoliation process. In addition, laminar heterostructures were created by combining two or more individual multi-layered films, such as MoS\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;MXene to explore their impact on shielding properties. The X-ray shielding performance at low- energy X-rays (30 kVp) was investigated for all prepared films (experimental set-up \u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e) and compared with that of their complementary films composed of bulk structures using the same mass.\u003c/p\u003e"},{"header":"2 Experimental","content":"\u003cp\u003e \u003cb\u003e2.1 Chemicals and materials\u003c/b\u003e: Molybdenum disulfide powder (MoS2, 99.99%, 23 \u0026micro;m) and sodium bromide (NaBr) was purchased from Chem-Supply (Australia). Bulk crystalline antimonene (Sb) with 99.9% purity was purchased from Smart Elements, Austria. The Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e MAX was supplied by Carbon-Ukraine. Carboxymethylcellulose sodium salt (CMC, high viscosity) and isopropanol (reagent grade, \u0026ge;\u0026thinsp;99.5%) was provided by Sigma-Aldrich (Australia).\u003c/p\u003e\u003cp\u003e \u003cb\u003e2.2 Preparation of 2D materials\u003c/b\u003e: Bulk MoS\u003csub\u003e2\u003c/sub\u003e powder was exfoliated into single layer MoS\u003csub\u003e2\u003c/sub\u003e sheets using a Planetary Ball Mill PM 200 (Retsch, Australia) with zirconium balls (3 mm in diameter)3 [30]. NaBr was added to facilitate the process of the ball milling with a weight ratio of NaBr: MoS\u003csub\u003e2\u003c/sub\u003e at 20:1, and the weight ratio of balls to powder was also 20:1. After the dry ball milling process, NaBr in the as-prepared mixture was removed by washing several times using distilled (DI) water with the aid of a centrifuge (Sigma, Australia, 4200rpm) and then dried in oven at 50℃ overnight for the further step.\u003c/p\u003e \u003cp\u003eThe synthesis steps of 2D MXene nanosheets was performed followed a literature guideline [23,28,31] Briefly, the small pieces of Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e MAX phase were ground into fine powders using a mortar, and the powders having a particle size of less than 25 \u0026micro;m were selected by a 25 \u0026micro;m sieve and collected for further use. Lithium fluoride (1.5 g) was added to 20 ml of 9M HCl solution in a reaction vessel under and stirred with a magnetic bar, then 1 gram of Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e was slowly added into the solution. The mixture was maintained in an oil bath environment at 35 \u0026ordm;C for 24 h. After the etching reaction was completed, the reacted mixture was subjected to centrifugal washing with deionized H2O at 3500 rpm for 30 minutes. This washing procedure was repeated 5 to 6 times until the pH value reached around 6, and a relatively pure Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e x product (MXene) was obtained. After washing, the product was ultrasonically separated to obtain a two-dimensional layered MXene material. A small amount of MXene powder was obtained by drying the raw MXene material, and its electrical conductivity was tested.\u003c/p\u003e \u003cp\u003eFew-layer antimonene (FL-Sb) nanosheets were prepared in a 4:1 isopropanol/water mixture by exfoliating bulk Sb crystals using a combination of ball milling and ultrasonication [29]. Bulk Sb crystals were put in a zirconia milling pot with isopropanol/water solvent. The samples were then ball-milled using Retsch planetary ball mill (PM 200) with zirconia balls (1 mm) at 300 rpm for 30 min. After drying, the ball-milled Sb flakes (30 mg) were re-dispersed in 4:1 isopropanol/water mixture (10 mL) for further exfoliation. The exfoliation was carried out in a bath ultrasonication for 40 min. Then the resulting black suspension was centrifuged at 3000 rpm for 3 min, and the dark grey supernatant was recovered.\u003c/p\u003e \u003cp\u003e \u003cb\u003e2.3 Preparation of 2D multi-layered films and their laminar heterostructures\u003c/b\u003e: Few-layer exfoliated MoS\u003csub\u003e2\u003c/sub\u003e were dispersed with DI water and then bath-sonicated for 1 h, respectively. CMC solution (0.5 wt.%) was added to the as-prepared MoS\u003csub\u003e2\u003c/sub\u003e solution with the optimized weight ratio to prepare dispersion with known MoS2 concentration of 10 mg/ml. The mixture was then stirred constantly for 3 h at the room temperature (20\u0026thinsp;\u0026plusmn;\u0026thinsp;2 ℃) followed by composed of multi-layered structures of assembled MoS\u003csub\u003e2\u003c/sub\u003e sheets. The prepared MoS\u003csub\u003e2\u003c/sub\u003e film was then dried for 12 h in air at the room environment (20\u0026thinsp;\u0026plusmn;\u0026thinsp;2 ℃) and used as a freestanding film for X-ray experiments. The mass loading and thickness of the film was measured to be consistent with prepared films using other 2D materials.\u003c/p\u003e \u003cp\u003eThe MXene films were produced by the same method of vacuum filtration as following details using MXene dispersion in deionized water that was sonicated for 1 hour before filtration. Required volumes (2 ml to 8 mL) of as-prepared MXene solutions were slowly filtrated by a vacuum filtration system to form MXene layered films on the membranes. The MXene-deposited membrane connected to the suction filter was placed in a vacuum drying oven and dried at 40\u0026ordm;C for 12 h. After that, the entire system was taken out from the vacuum drying oven, the suction filter was removed, and then the dried MXene film was carefully separated from the membrane and used for X-ray measurements.\u003c/p\u003e \u003cp\u003eSimilar process was applied to make 2D antimonene multi-layered films using prepared 2D FL-Sb dispersion with known concentration and volume to achieve with the same mass loading as 2D MoS\u003csub\u003e2\u003c/sub\u003e and 2D MXene films. Double laminar heterostructure films were prepared by stacking individual 2D MoS\u003csub\u003e2\u003c/sub\u003e layered film and individual 2D MXene layered film into one combined structure (MoS\u003csub\u003e2\u003c/sub\u003e/MXene). Quadrupole laminar heterostructure films were prepared by double stacking individual 2D MoS\u003csub\u003e2\u003c/sub\u003e layered films and individual 2D MXene layered films into the combined structure (MoS\u003csub\u003e2\u003c/sub\u003e/MXene/ MoS\u003csub\u003e2\u003c/sub\u003e/MXene).\u003c/p\u003e\u003cp\u003e \u003cb\u003e2.4 Characterizations\u003c/b\u003e: A scanning electron microscope (SEM-FEI Quanta 450, Japan) in a low vacuum chamber at an accelerating voltage of 5 kV. The average thickness and particle topography of exfoliated FL-Sb was examined using an NT-MDT Ntegra Solaris Atomic Force Microscope (AFM) via tapping mode. NT-MDT SPM Software (Nova 1.0.26) was used for AFM image processing. A particle size analyzer from Malvern instrument (NanoSight NS300) was used to examine the average particle size distribution. A transmission electron microscope (TEM, FEI Titan Themis) was used to acquire nanoscale morphology and elemental analysis of exfoliated substances. Thermogravimetric analysis (TGA) of FL-Sb, PDMS and their composite were studied using Mettler-Toledo TGA/DSC 2, Switzerland in an air atmosphere at a constant heating rate of 5\u0026deg;C/min. The vibrational stretching modes of different molecular bonds in PDMS modified samples were studied by Fourier transform infrared spectroscopy (FTIR) (Nicolet 6700 Thermo Fisher, USA).\u003c/p\u003e\u003cp\u003e \u003cb\u003e2.5 X-ray radiation measurements\u003c/b\u003e: X-ray transmission testing was performed using a superficial X-ray tube (SXR) unit (Gulmay D3150, UK) as shown in \u003cb\u003eFigure S7.\u003c/b\u003e The distances between the X-ray tube and sample-placing panel and sample-placing panel to the detector were equally 50 cm. The samples were exposed to the X-ray voltage range at 30, 50, 80, 100 kVp, respectively, for 0.50 min with the X-ray transmitted sample placing area of diameter at 1 cm, and the X-ray attenuation performance was evaluated as the transmission dose of samples divided by the transmission dose without the sample. Each sample was measured 3 times and determined by the arithmetic mean. The X-ray attenuation of an X-ray beam is expressed as a function of the linear attenuation coefficient (\u0026micro;) and calculated using equation and procedure as reported elsewhere.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Fabrication and characterization of prepared multi-layered structures of 2D materials\u003c/h2\u003e \u003cp\u003eComprehensive physical, chemical and thermal characterization of the synthesized few-layers MoS\u003csub\u003e2\u003c/sub\u003e sheets, antimonene and MXene and their layered films are summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cb\u003eFigure S2-S4.\u003c/b\u003e A ball-milling method was employed to exfoliate a large quantity of micron sized MoS\u003csub\u003e2\u003c/sub\u003e sheets with an average particle size of 22 \u0026micro;m (\u003cb\u003eFigure S2\u003c/b\u003e) into few-layers nanosheets with an average particle size of 432 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cb\u003eFigure S2\u003c/b\u003e). The corresponding SEM and TEM image (\u003cb\u003eFigure S2\u003c/b\u003e (a) and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) confirmed the presence of the sheet-like MoS\u003csub\u003e2\u003c/sub\u003e structure with significant changes in their particle size and morphology. High-resolution TEM images showed exfoliated MoS\u003csub\u003e2\u003c/sub\u003e nanosheet with ~\u0026thinsp;7 layers (inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. Raman, XRD, and FTIR analyses (\u003cb\u003eFigure S2\u003c/b\u003e) confirmed their significant differences from that of bulk MoS\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFew-layers MXene was prepared using a common etching process from Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e MAX phase materials as described in the literature [25\u0026ndash;26]. Their typical structure characterized by SEM and TEM is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and \u003cb\u003eFigure S2\u003c/b\u003e confirms a few-layer structure of MXene with the dimension of a few hundred nanometers. Few-layer 2D antimonene (FL-Sb) nanosheets were synthesized in a 4:1 isopropanol/water mixture by exfoliating bulk Sb crystals using a combination of ball milling and ultrasonication, and the structural differences before and after exfoliation are summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec \u003cb\u003eand Figure S3.\u003c/b\u003e The exfoliation of bulk-Sb (30\u0026ndash;45 \u0026micro;m, \u003cb\u003eFigure S3a\u003c/b\u003e transforms it into nanosheets (confirmed by TEM in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec \u003cb\u003eand Figure S3c\u003c/b\u003e) with an average lateral dimension ranging between 300\u0026ndash;400 nm (confirmed by particle size distribution \u003cb\u003eFigure S3d\u003c/b\u003e). Figure S3e presents the powder diffraction pattern of exfoliated FL-Sb nanosheets showing typical signature of Sb nanopowder, which is in good agreement with the standard diffraction card \u0026ldquo;JCPDS no. 01-085-1324\u0026rdquo;. These 2D sheet structures dispersed in solution, were used to fabricate their multi-layered films by a vacuum filtration process. During this process 2D sheets were self-assembled into a layered film structure and their typical cross-section SEM images are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed-f. These images clearly confirm the formation of their layered film structure composed of thousands of layers assembled 2D sheets that is supposed have a strong Van Der Waals interaction between layers. It is worth nothing that these layered films can be prepared with the controllable thickness from tens to several hundreds of microns including making their heterostructure films by combining different 2D materials.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.2 X-Ray shielding performance of multi-layered structures of 2D materials\u003c/h2\u003e \u003cp\u003eThe study on X-ray transmission and the attenuation enhancement of the prepared individual 2D MoS\u003csub\u003e2\u003c/sub\u003e, MXene and antimonone layered films compared to their corresponding bulk films are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e. These results showed a significant decrease in the X-ray transmission of the 2D layered films at 30 kVp, compared to their bulk counterparts. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb confirmed that the X-ray attenuation enhancement rate of 46.67% for MoS2 film, 37.28% for 2D antimonene enhancement rate of 46.67% for MoS\u003csub\u003e2\u003c/sub\u003e film, 37.28% for 2D antimonone film and 41.07% for MXene film is achieved compared to their bulk films. It is worth noting that the mass loading of all the prepared films including controls had a similar mass (g/m\u003csup\u003e2\u003c/sup\u003e), to make the observed results related only to differences in mass or density. The results obtained at a lower X-ray energy of 30 kVp are presented where the X-ray attenuation enhancement difference is the most significant and relevant. However, the X-ray transmission measurements at the higher energy of 50 kVp and 80 kVp were also performed showing the same trend, but with lower shielding enhancement (data not shown) indicating this phenomenon is more prominent at lover energies. To improve the shielding performance at higher energies a combination with other materials should be considered.\u003c/p\u003e \u003cp\u003eIt is well known that that X-ray shielding is dependent on the thickness of the material and by increasing the thickness of these 2D multi-layered films, it will be possible to further improve their performances. This optimization was further demonstrated by controlling the film thickness in case of MoS\u003csub\u003e2\u003c/sub\u003e layered films prepared with different thickness or masses per surface area. \u003cb\u003eFigure S5\u003c/b\u003e presents the X-ray transmission results showing that by increasing their thickness of the MoS\u003csub\u003e2\u003c/sub\u003e films from 0.11 mm to 1.34 mm this could effectively attenuate the X-ray transmission down to 0.09%. The X-ray transmission value of the exfoliated MoS\u003csub\u003e2\u003c/sub\u003e film with the optimized thickness of 1.34 mm was further evaluated compared with 0.20 mm Pb sheet indicating comparable performance to 0.20 mm Pb-equivalent attenuation at 30 kVp (inset of \u003cb\u003eFigure S5\u003c/b\u003e). Although the optimized thickness (1.34 mm) of layered 2D MoS\u003csub\u003e2\u003c/sub\u003e film was much thicker than the 0.20 mm Pb sheet, the weight of this film (minus the holding substrate) at 1.18 g was 50% lighter than the 0.20 mm Pb (2.17 g). This can be defined as outstanding results and comparable to Pb benchmark materials indicating layered 2D materials as very promising solution for the development of new generation of lightweight and Pb-free shielding materials for broad protection applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.3 X-Ray shielding performance of multi-layered and laminar heterostructures\u003c/h2\u003e \u003cp\u003eIn the following experiment the X-ray radiation shielding performance of the films with multi-layered and laminar heterostructure of 2D materials prepared by combining two or more individual multi-layered films such as MoS\u003csub\u003e2\u003c/sub\u003e and MXene was explored. One combination of these double laminar multi-layered films was made using the MoS\u003csub\u003e2\u003c/sub\u003e film on the top and the MXene film on the bottom (MoS\u003csub\u003e2\u003c/sub\u003e/MXene). The second was composed by the MoS2 and MXene films subsequently ordered as quadruple laminar heteostructures (MoS\u003csub\u003e2\u003c/sub\u003e/MXene/MoS\u003csub\u003e2\u003c/sub\u003e/MXene). Comparison of obtained X-ray transmission results on these films are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The results showed that the double laminar heterostructures have increased X-ray shielding enhancement to their individual multi-layered for 12.85% MoS\u003csub\u003e2\u003c/sub\u003e and 6.62% MXene with the same mass loading. However, the films with quadruple laminar heterostructure multi-layered films showed further significant shielding of 62.26% for MoS\u003csub\u003e2\u003c/sub\u003e and 59.57% for MXene compared to their films composed with individual multi-layers. By changing the orientation of these laminates such MXene at the top/ MoS\u003csub\u003e2\u003c/sub\u003e on bottom or reverse no difference was observed. These results suggest possible synergetic effect with increasing number of laminates from 2 to 4 that was surprising, that is possibly, caused by an additional scattering of X-rays at the interface between these laminated structures. However, more studies are needed to understand the mechanism of these enhancements by heterostructures. These results suggests that by increasing number of laminates of the 2D multi-layered films we could further enhance shielding performance. This is another promising strategy to further improve the X-ray shielding performance, which deserves to be explored in the future with studies and details.\u003c/p\u003e \u003cp\u003eThese presented results clearly reveal experimental evidence that multi-layered 2D materials and their laminar heterostructures can enhanced X-ray shielding showing new properties not observed before. To provide theoretical validation of this experimental evidence we try to perform the Monte Carlo simulation used for modelling of X-ray attenuation of bulk materials. However, our attempt to perform theoretical simulation by the Monte Carlo simulation to predict these properties was not very successful. Main reason was because of the high complexity of the model to describe the multi-layered and laminar heterostructures of 2D materials used in our study. So far, conventional physical models consider uniform bulk structure where shielding is dependent of parameters such as Z atomic number, density and the film thickness and there has been no simulation model for the interaction with multi-layered 2D structures. The complexity of this model is related to consideration of many parameters such as the size and morphology of individual 2D crystal sheets, number of their atomic layers, their crystallinity, number and layers in the film, their interlayer distances, Van Der Waals interactions between layers, the interfaces between laminated structures, number of laminates etc. The interaction of X-ray photons inside these multi-layered structures because of these parameters is reasonable to be different from that of the bulk structure of material. We expect these models will be developed in the future enabling to theoretically verify the experimental results presented in this paper and predict how to improve designing more optimized heterostructures and their combinations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe X-ray attenuation is known as the process of the X-ray intensity reduction via either absorption or scattering when X-ray photons pass through the shielding material [1\u0026ndash;2]. It involves three interaction mechanisms including (1) photoelectric effect, (2) Compton scattering, and (3) pair production [27]. To explain the observed attenuation results of the 2D layered materials, we assumed that the X-ray shielding performance could be enhanced because of multiple scattering and absorption occurring during the incoming X-ray photons that interacted with these layered films. This type of scattering process is less relevant within the bulk materials, where most of the deflection occurred on the top surface, as schematically presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The multi-layered 2D material films can increase the probability of photoelectric effect within each layer, inside the films leading to enhanced X-ray shielding ability. In other words, incident X-ray is absorbed and reflected many times between each layer (+\u0026thinsp;1000 layers) within the layered 2D material films which makes their attenuation properties much higher compared to non-layered and bulk materials. In terms of the combination of two or more 2D layered films and their heterolaminar structures, the multiple interfaces between each layer of the 2D laminates will provide additional scattering and absorption of X-ray photons multiple times as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. This is reasonable explanation for observed shielding enhancement, but more studies are needed to fully reveal the mechanism of X-ray interactions within these 2D layered heterostructures in addition to establishing their appropriate models to describe and predict these interactions for range of 2D materials with high Z number.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, the presented study practically demonstrates that the multi-layered films composed of 2D materials such as MoS\u003csub\u003e2\u003c/sub\u003e, MXene and antimonene and their laminar heterostructures can significantly attenuate low energy (30 kVp) X-ray rays. The phenomenon is explained as results of multiple scattering and absorption inside the 2D multi-layered film structures that is not occurred in bulk material. The X-ray shielding enhancement of 46.67% for layered MoS\u003csub\u003e2\u003c/sub\u003e, 37.28% for antimonene and 41.07% for MXene, was determined compared with their bulk counterparts. Further and surprising enhancement of X-ray shielding was achieved by combination of individual films such as MoS\u003csub\u003e2\u003c/sub\u003e and MXene to create heterostructure (double and quadruple laminates) showing 62.26% and 59.57% compared to their individual MoS\u003csub\u003e2\u003c/sub\u003e and MXene layered films. This paper presents exciting discovery about X-ray shielding properties of 2D materials and their heterostructures not considered before that will open a new horizon for designing a new Pb-free radiation shielding technology and their successful application across broad sectors in medicine, nuclear industry, space exploration, and defence. Further studies on the theoretical modelling on photon interactions with 2D multi-layered structures are needed to give more insights to understand this mechanism and help development of more advanced shielding structures.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eSupplementary Information:\u0026nbsp;The online version contains supplementary material presenting characterization results prepared 2D materials including TEM, SEM, EDAX, particle size. XRD, Raman spectroscopy measurements) is available at XXX\u003c/p\u003e\n\u003cp\u003eThere are no conflicts to declare. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eThe authors acknowledge the financial support from the ARC Research Hub for Graphene Enabled Industry Transformation, (IH150100003). We thank Australian Microscopy for the access of SEM, TEM facilities, Mr. Ken Neubauer, Dr. Ashley Slattery for their technical support on SEM and TEM measurements.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eE.B. Podgorsak, Radiation Physics for Medical Physicists, 2016, Springer Berlin, Heidelberg\u003c/li\u003e\n\u003cli\u003eM.E Noz, G.Q.Maguire, Radiation protection in health sciences. World Scientific, New York, 1999; \u003c/li\u003e\n\u003cli\u003eHughes, J. S.; Watson, S. J.; Jones, A. L.; Oatway, W. B. \u003cem\u003eJ Radiol Prot\u003c/em\u003e 2005; \u003cstrong\u003e25\u003c/strong\u003e (4): 493-6. DOI: 10.1088/0952-4746/25/4/010.\u003c/li\u003e\n\u003cli\u003eICRP, Radiological protection of people and the enviroment in the event of a large nuclear accident, 2020: 4.\u003c/li\u003e\n\u003cli\u003eJ.P. McCaffrey, E. Mainegra-Hing, H. 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Sci Rep\u003c/em\u003e 2021: \u003cstrong\u003e11\u003c/strong\u003e (1): 4384, DOI: 10.1038/s41598-021-83031-4.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"graphene-and-2d-materials-technologies","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Graphene and 2D Materials Technologies](https://www.springer.com/journal/41127)","snPcode":"41127","submissionUrl":"https://submission.springernature.com/new-submission/41127/3","title":"Graphene and 2D Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"2D materials, multi-layered structure, heterostructures, X-rays shielding","lastPublishedDoi":"10.21203/rs.3.rs-3076104/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3076104/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis paper demonstrates a new concept of using two-dimensional (2D) layered materials and their heterostructures for enhanced X-ray radiation shielding. This phenomenon is revealed by characterization the X-ray shielding performances of several 2D materials with high atomic numbers (Z) including MoS\u003csub\u003e2\u003c/sub\u003e, antimonene (Sb), and MXene prepared as multi-layered and heterostructured films by assembly of their few-layer (FL) sheets. \u0026nbsp;Results showed considerable X-ray shielding enhancement of (40-50 %) at 30kVp for individual 2D multi-layered films compared with their bulk structures of these materials. Furthermore, when these multi-layered films were combined into laminar heterostructures structures (e.g. MoS\u003csub\u003e2\u003c/sub\u003e+MXene) further enhancement of ca 60 % was achieved. The mechanism of the observed X-ray shielding enhancement by these multi-layered 2D structures is not clear at this stage. It is postulated to be the result of an additional multiple scattering and reflections of photons between multiple layers of 2D crystals inside the film, that is not occurred in uniform bulk material. The presented results suggest that multi-layered 2D materials with high atomic numbers (Z) and their laminar heterostructures can offer a new and promising strategy for designing of a new generation of Pb-free radiation-shielding materials that is urgently needed across broad sectors.\u003c/p\u003e","manuscriptTitle":"Revealing enhanced X-Ray radiation shielding of 2D layered materials and their laminar heterostructures","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-06-26 19:03:55","doi":"10.21203/rs.3.rs-3076104/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2023-07-05T19:20:01+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2023-06-24T17:20:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"8de7d6ba-c1d4-4358-a66e-d1d4e645eb48","date":"2023-06-19T20:51:17+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-06-19T19:53:21+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-06-19T19:36:44+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-06-19T14:00:57+00:00","index":"","fulltext":""},{"type":"submitted","content":"Graphene and 2D Materials","date":"2023-06-17T13:48:42+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"graphene-and-2d-materials-technologies","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Graphene and 2D Materials Technologies](https://www.springer.com/journal/41127)","snPcode":"41127","submissionUrl":"https://submission.springernature.com/new-submission/41127/3","title":"Graphene and 2D Materials","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"5cef51b5-be6e-4cf4-868b-6f73ef74fb86","owner":[],"postedDate":"June 26th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-16T15:06:49+00:00","versionOfRecord":{"articleIdentity":"rs-3076104","link":"https://doi.org/10.1007/s41127-023-00064-4","journal":{"identity":"graphene-and-2d-materials-technologies","isVorOnly":false,"title":"Graphene and 2D Materials"},"publishedOn":"2023-10-13 15:01:58","publishedOnDateReadable":"October 13th, 2023"},"versionCreatedAt":"2023-06-26 19:03:55","video":"","vorDoi":"10.1007/s41127-023-00064-4","vorDoiUrl":"https://doi.org/10.1007/s41127-023-00064-4","workflowStages":[]},"version":"v1","identity":"rs-3076104","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3076104","identity":"rs-3076104","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}