Unlocking exceptional EMI shielding in Ti₃C₂T_x MXenes through controlled microstructure and surface chemistry

Shahzad Hussain*^a, Resham Siddique^a, Muhammad Nadeem^b, Eman Zafar^a, Sadia Manzoor^a and Jawwad A. Darr^c
aMagnetism Lab, Department of Physics, COMSATS University Islamabad, 44000, Pakistan. E-mail: shahzad.hussain@comsats.edu.pk
^bPolymer Composite Group, Directorate of Science, PINSTECH, Nilore, 44000, Pakistan
^cDepartment of Chemistry, University College London, UK

First published on 4th August 2025

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Introduction

Electromagnetic interference (EMI) shielding materials are gaining importance because of the urgent demand for electromagnetic compatibility of modern equipment and protection of living tissue from hazardous radiation.^1–3 It is desirable to have high-performance electromagnetic shields with high EMI shielding efficiency (SE), low thickness and weight, superior mechanical strength and flexibility, and good stability.^4,5 Low-dimensional nanomaterials such as metal nanowires, carbon nanotubes (CNTs), graphene, or surface functionalized atomically thin layer transition metal carbides or nitrides (known as MXenes), offer great potential for bottom–up construction of EMI shielding macrostructures and devices due to their good electrical conductivity and high aspect ratios.^6–10 Among these materials, 2D MXene thin sheets with the formula Ti₃C₂T_x (T = O, OH, F, etc.), have garnered attention for producing high-performance EMI shielding materials due to their metallic conductivity and solution processability, resulting from their hydrophilic functional groups (O, OH, F, etc.).¹¹ For instance, vacuum-filtered MXene films with a thickness of 11 μm demonstrated a good EMI SE of 68 dB, resulting in an ultrahigh absolute shielding effectiveness (SSE_T) of 25863 dB cm² g⁻¹, compared to solid metallic copper or stainless steel, with SSE_T values of ca. 30 dB cm² g⁻¹.¹² In another study, an EMI shielding effectiveness of 92 dB at a thickness of 45 μm in the X-band frequency range ( 8.2 to 12.4 GHz), was observed, showing exceptional promise for applications in modern smart devices.¹² This shielding efficacy of Ti₃C₂T_x MXene films is ascribed to their intrinsic electrical conductivity (4500 S cm⁻¹), numerous surface terminations, and laminate architecture, as supported by the theoretical study by Schultz et al.¹³ Hence, it is important to optimize and understand correlations between these parameters to design an EMI shield with high shielding effectiveness.

The intrinsic features of Ti₃C₂T_x, such as metal-like electrical conductivity, are influenced by a variety of parameters, including defect density,¹⁴ flake size,¹⁵ surface functional groups of synthesized MXene flakes and intercalant type.¹⁶ These parameters also directly affect the oxidation kinetics of the produced MXenes. Dong et al.¹⁷ suggested that the surface terminations produced during MXene synthesis, are expected to modulate metal-to-insulator transitions and influence functional properties such as magnetism, Li-ion capacity, mechanical properties, and shielding effectiveness.^18–20 To date, chemical etching of Ti₃AlC₂ (a type of MAX phase with general formula M_n+1AX_n where n = 1 to 4, M is an early transition metal, A can typically be a Group 13 or 14 element and X is carbon in this case, but can be nitrogen in other cases) using fluoride-based acids or salts (such as HF and LiF/HCl), has been a simple method for preparing 2D MXene Ti₃C₂T_x (T = O, OH, F). These traditional etching chemicals can react selectively with the Al layer and remove the resulting AlF₃ from the interlayer space and introduce various functional groups.²¹ However, it has been noticed that harsh etching conditions in the case of HF (strong acid), can induce additional structural defects in MXenes and promote their degradation to metal oxides such as TiO₂.²² In contrast, mild etchants such as LiF + HCl, can produce better quality sheets with greater stability of MXene sheets in an aqueous dispersion (Fig. S2). Hence, a comparative investigation is necessary to determine the impacts of either mild or hard etching conditions on the EMI shielding capabilities.

The porosity, flake size and alignment of highly conductive nano-layered structures are expected to have a significant impact on EMI shielding characteristics.²³ Liu et al.²⁴ showed that creating a porous structure between Ti₃C₂T_x nanosheets, can increase d-spacing to a greater extent and can significantly reduce stacking of sheets, leading to better attenuation of electromagnetic waves. It is typically possible to acquire the porous morphology of thin films assembled with nanoparticles at the pre-forming or post-treatment stages. Zhao et al.²⁵ obtained a porous structure by incorporating polymethyl methacrylate (PMMA) microspheres between Ti₃C₂T_x nanosheets, which were then removed at 450 °C. Moreover, porous foams and aerogels, as well as segregated structures, have shown improved shielding performance.^26,27 Recently, highly aligned graphene/polymer nanocomposites were found to have significantly improved shielding efficiency.²³ Hence, by controlling the microstructure of multilayered Ti₃C₂T_x thin films, shielding properties can be improved. Thus, while designing MXenes for EMI applications that require high electrical conductivity, porous structure, and dipole losses, careful control over the influencing factors is essential.

In the present work, shielding properties have been investigated for a range of parameters, including etchant type, surface chemistry, flake size, microstructure, thickness, and Ti₃C₂T_x (T = O, OH, Cl, F) loading. The thickness of films was varied to tune the EMI shielding effectiveness over a wide range where 60 dB (99.9999% shielding efficiency) was obtained for a 14 μm film with an excellent absolute shielding effectiveness (SSE_T) of 53210 dB cm² g⁻¹. In addition, a robust, freestanding Ti₃C₂T_x film that underwent heat treatment in an inert environment and had a thickness of only 5 μm, demonstrated an X-band EMI SE of 71 dB, which was approximately 37% higher than that of the pristine film. Thus, it outperforms previous freestanding MXene-based films with an ultrahigh SSE_T value of 72300 dB cm² g⁻¹ at comparable thickness, which is attributed to anomalously high absorption of electromagnetic waves due to a significant change in the layered structure (metamaterial-like structure) as evident form SEM studies.

Motivated by the high shielding efficiency results of thin films, cotton fabric (CF) was also chosen as a substrate to coat the conductive dispersion because Ti₃C₂T_x is polar in nature and has a negatively charged surface that supports good adhesion with cellulose (C₆H₅O₁₀)_n-based fabrics (cotton, linen, etc.).²⁸ CF was coated with two different loadings of Ti₃C₂T_x, resulting in a total shielding effectiveness of 82 dB (among the highest for synthetic materials of comparable thickness). The EMI SE was retained even after six months by storing the fabric under ambient conditions (open to air). Both the fabric properties (porosity, high yarn density and weave pattern) as well as the high electrical conductivity and layered structure of the MXene have clearly contributed to the exceptional EMI SE performance. Indeed, the results presented here fulfil all the desired performance criteria for telecommunications, detection systems, defense, and aerospace applications.

Methods

Materials and chemicals

Hydrochloric acid (HCl, 37% purity) was obtained from Riedel-de Haen; lithium fluoride (LiF), and MAX powder (Ti₃AlC₂) were bought from Aladdin Biochemical Technology (Shanghai, China). The non-sterile, hydrophilic PVDF membranes (pore size 0.45 μm) were obtained from Durapore (Fig. S1). Cotton fabric (CF) was bought from the textile industry (The Crescent Textile Mills Ltd). Without any further purification, all reagents were used as it is in the following protocol.

Amalgamation of chemically exfoliated 2D MXene (Ti₃C₂T_x) nanosheets

The etching and the delamination procedure of Ti₃C₂T_x nanosheets is shown by a schematic diagram in Fig. 1(a). Minimally intensive layer delamination (MILD), a top–down facile approach was used to prepare a green colloidal dispersion of single delaminated Ti₃C₂T_x sheets.²⁹ This method is unique as it is easy to process, retains the size and properties of the flakes and expands the production and scalability of the exfoliated Ti₃C₂T_x dispersion. A milder etchant, a combination of HCl + LiF, was used for ‘Al’ etching and successful exfoliation of titanium carbide sheets. In a typical procedure, 3M LiF was added into 37 wt% concentrated HCl in a Teflon-lined beaker and mixed at 400 rpm for 10 min. Then, 2 g of Ti₃AlC₂ was added gradually over 15 minutes into it and the temperature was maintained at 38 °C for 48 h to completely etch the Al layer. The resultant slurry was centrifuged several times with deionized water until the pH value of the supernatant was in the range of 6 to 7. After achieving a neutral pH of the supernatant, the resultant sediments were again diluted with deionized water and sonicated in an ice bath for 1 h to obtain the exfoliated nanosheets. The Ti₃C₂ nanosheet dispersion was again centrifuged at 3500 rpm for 10 minutes to remove impurities. A green colored stable colloidal solution was attained which confirmed the successful etching of ‘Al’ and exfoliation/delamination of Ti₃C₂ nanosheets.³⁰

The chemical reaction during the whole process was as follows:³¹

Ti3AlC2 + 3LiF + 3HCl → Ti3C2 + AlF3 + 3LiCl + (3/2) H2	(1)

wherein Ti₃AlC₂ was the MAX powder and LiF and HCl were used as the etchant. H₂ gas was released during the reaction and AlF₃ and LiCl salts were removed during washing, leaving behind suspended multilayer stacked sheets of Ti₃C₂. Hydrofluoric acid (HF) can also be used as an etchant (Fig. S2); however it is a strong acid that can damage the flakes of Ti₃C₂ (Fig. S3). Furthermore, in the next processing step, dimethyl sulfoxide (DMSO) delamination is required to obtain a stable colloidal dispersion.³² The authors also etched Al using HF acid and fabricated thin films with both LiF + HCl and HF etched solution, to study the effect of different etchants on flake size and consequently, on EMI shielding properties. The details of the HF etching procedure are given in the supplementary data file.

Preparation of freestanding Ti₃C₂T_x thin films

Free-standing Ti₃C₂T_x thin films of different thicknesses were fabricated using a vacuum filtration approach. A substrate, either PVDF filter paper or cotton fabric, was placed on a porous plate of the filtration setup and the Buchner funnel was filled with a specific concentration of the prepared colloidal solution. The vacuum filtration process left the nanoparticles on top of the substrate, while removing the liquid from the colloidal solution, which was then discarded. The obtained Ti₃C₂T_x thin films were dried in a vacuum oven at 60 °C to get thin, flexible, shiny, and light weight films. The filtration assembly and fabricated thin films are shown in Fig. 1(b).

Coating of 2D MXene (Ti₃C₂T_x) nanosheets onto cotton fabric

Before coating, the fabric was dried in an oven at 70 °C to remove moisture. The cotton fabric was cut in dimensions of 8.6 × 7.4 cm and then a specific amount of the dispersion was deposited onto it by vacuum filtration. In this case, cotton functioned as a filter membrane while the presence of carboxyl or hydroxyl groups on the surface of cotton helped in the loading of the dispersion. In the next step, only one side of the fabric was coated with half of the dispersion and dried in a vacuum oven for 4 h at 60 °C. When one side was completely dried, then the other side was coated and dried again in a vacuum oven for 4 h at 60 °C. The loaded cotton fabric was still flexible, lightweight, and had good mechanical strength under moderate stretching. The same strategy and conditions were applied to another cotton fabric, which was coated with a different loading. The loading was determined by measuring the total mass before and after coating.

The loading was calculated using the following formula.

Loading (mg mL−1) = mass of coated cotton fabric − mass of uncoated cotton fabric	(2)

Material characterization

The crystal structures of Ti₃AlC₂ and Ti₃C₂T_x were identified through powder X-ray diffraction (XRD) using monochromatic Cu Kα radiation (λ = 1.5405 Å) using a voltage of 40 kV at a scan rate of 1° min⁻¹ in the scanning angle 2θ range of 0 to 60°. The stability of the Ti₃C₂T_x dispersion was analyzed using a zeta-sizer nano ZS apparatus (Malvern Panalytical, UK). Dynamic light scattering (DLS) measurements were performed to study the size distribution of 2D Ti₃C₂T_x sheets, by using a back-scattered light detector operated at an angle of 173°. The morphology and microstructure of the delaminated/exfoliated Ti₃C₂T_x thin film as well as cotton fabric, was analyzed using a field emission scanning electron microscope (FE-SEM) and EDS measurements were also performed (Fig. S4 and Table S1). The electronic structure was examined by X-ray photoelectron spectroscopy by using an incident beam from an Al X-ray source (1486.5 eV) operated at 10 kV, 10 mA, and 100 W for both survey and high-resolution scans. The EMI shielding properties of Ti₃C₂T_x thin films and cotton-coated Ti₃C₂T_x, were measured through a vector network analyzer at room temperature using the waveguide method within 8–12 GHz (X-band). Scattering parameters S₁₁ or S₂₂ (reflection coefficient data) and S₁₂ or S₂₁ (absorption coefficient data) were recorded and used to calculate the reflection coefficient (R), absorption coefficient (A), and transmission coefficient (T) as follows.

R = |S11|2 = |S22|2	(3)

A = 1 − R − T	(4)

T = |S12|2 = |S21|2	(5)

The total shielding effectiveness (SE_T), shielding effectiveness due to reflection (SE_R), shielding effectiveness due to absorption (SE_A), attenuation percentage (shielding efficiency) and effective absorption percentage (abs %), can be calculated by using the following formula.

SET = SEA + SEMR + SER	(6)

SE_MR can be ignored when SE_T ≥ 15 dB.³³

SER = −10log(1 − R)	(7)

	(8)

	(9)

	(10)

For non-magnetic and highly conductive shields, the SE_A and SE_R can be written as

	(11)

	(12)

where, σ, t and f are the electrical conductivity, thickness of shield and frequency of electromagnetic waves, respectively. These equations indicate the strong dependence of shielding parameters on electrical conductivity.

Results and discussion

Zeta potential and dynamic light scattering measurements (DLS) were performed to examine the colloidal properties of Ti₃C₂T_x nanosheet dispersions as shown in Fig. 2. Ti₃C₂T_x flake dispersions in water showed colloidal stability and homogeneity without the addition of any surfactant, at pH values ≥6. The stability and homogenous suspension of Ti₃C₂T_x flakes in water are due to the negatively charged Ti₃C₂ nanosheets, which are induced by the presence of functional groups (e.g., OH, F, and Cl). In particular, F and Cl anions are highly electronegative, making the surface of sheets more negative.³⁴ Fig. 2(a) shows that the aqueous Ti₃C₂T_x mixture (pH value ≥6) had a large negative zeta potential of −32.1 mV, which confirmed the colloidally stability of the Ti₃C₂ nanosheet dispersion due to electric double layer compression.³⁵ Fig. 2(b) on the hand shows the variation of zeta potential indicating a large negative potential with increased pH. Under acidic conditions, the low zeta potential caused flocculation of Ti₃C₂T_x flakes (suspension physically unstable) due to weak repulsive charge that was not sufficient to overcome van der Waals attractive forces.³⁶ Thus, the dispersion was maintained at pH values ≥6. Higher colloidal stability was also observed for Ti₃C₂T_x nanosheet suspensions that were made by etching with mild acid (LiF + HCl) as compared to strong hydrofluoric acid (Fig. S2(a) and (b)).

Flake size is known to be a crucial factor affecting the electrical conductivity of a system, which in turn determines its EMI shielding properties.³⁷ The larger the flake size, the better will be the contact between the flakes, and the higher will be the conductivity.³⁷ Fig. 2(c) shows the DLS flake size distribution of Ti₃C₂T_x nanosheets with an average flake size of ca. 615 nm. As discussed in the zeta potential studies, the degradation mostly occurred at the edges of nanosheets, which was linked to the size of the flake and was most pronounced for small flakes. It was also shown that large flakes of Ti₃C₂T_x formed more stable dispersions.^34,38 Larger flake sizes were observed after the LiF + HCl treatment as compared to HF acid treated solutions (Fig. S3) and both dispersions were used for thin film fabrication. The small peak in the size distribution data in Fig. 2(c) not only gives information about the size of small flakes, but also demonstrates the size of solvent molecules i.e., water or the thickness of the nanosheets. Based on the working principle of DLS, the incident light falls on the surface or edges of the flakes and scatters to give information about the average flake size as well as their thickness.³⁹ The Tyndall effect was distinctly visible, displaying a uniform and stable, well (or evenly) dispersed green-colored Ti₃C₂T_x colloidal solution in water because of terminal surface functional groups e.g., OH, F, Cl, etc.^40,41

Fig. 3(a) shows the diffraction patterns of the parent MAX powder (Ti₃AlC₂) and M5 (5 μm) free standing Ti₃C₂T_x films (both without and after heat treatment); the data were taken at room temperature in the 2θ range of 5 to 65°. The characteristic diffraction peaks of Ti₃AlC₂ were located at 2θ values of 9.4°, 19°, 34°, 38°, 41.6°, 48.3°, 56.1° and 60.1° corresponding to (002), (004), (101), (104), (105), (110) and (202) planes, consistent with the literature.⁴² After eliminating the Al layer, the diffraction pattern of Ti₃C₂T_x was free of almost all diffraction peaks of Ti₃AlC₂ except the (002) peak at 2θ ≈ 6°, indicating successful etching of Al atoms. Moreover, the appearance of small diffraction peaks corresponding to (004), and (006) planes, indicates the multilayer nature of Ti₃C₂T_x films.⁴³ Hence, the selective extraction of ‘Al’ atoms from Ti₃AlC₂ when using a mild etchant mixture of HCl and LiF for 48 h, ensured a successful transition from the block multilayer structure of Ti₃AlC₂ into the accordion-like layered structure of Ti₃C₂T_x as shown in Fig. 3(b). Furthermore, the (002) diffraction peak became broader, weaker, rougher, and shifted to lower angles, from 9.4° to 6° in 2θ, after the etching process.⁴⁴ This shift may be attributed to the formation of Ti₃C₂ basal planes and an increase in the interlayer d-spacing from ca. 1.8 to 6.6 Å along the [0001] direction (an increment in the c-axis). The expansion of d-spacing was due to the presence of intercalants and an increase in the spacing between Ti₃C₂T_x flakes.^12,40 Moreover, some functional groups, T_x (OH, F, or Cl) might have been attached to the surface or edges of Ti₃C₂ nanosheets. These results suggested successful etching of Ti₃AlC₂ as well as the exfoliation/delamination of Ti₃C₂T_x.^45,46 The same film was annealed at 300 °C for four hours to understand the effects of temperature on the internal structure and on EMI shielding properties. A slight increase in 2θ values was observed, indicating a decrease in interplanar spacing due to the removal of functional groups.

The information regarding the surface chemistry, stacking, and quality of Ti₃C₂T_x, was obtained using Raman spectroscopy. Fig. 4(e) and (f) compares the Raman shift, revealing characteristic peaks at wavenumbers associated with Ti₃C₂T_x vibrations, and their respective surface functionalization for Ti₃C₂T_x films, before and after heat treatment. The vibrations of Ti₃C₂T_x consisted of E_g (in-plane) and A_1g (out-of-plane) peaks from both Ti and C atoms, consistent with the literature.⁴⁷ The spectrum was divided into three regions; (i) the flake region, which represented group vibrations of carbon, two titanium layers, and functional groups, (ii) the T_x region, which denoted surface group vibrations and, (iii) the carbon region (C region) that included both in-plane and out-of-plane vibrations of the carbon atoms. The A_1g peaks at 198 cm⁻¹ and the E_g peaks at 247, 286, and 382 cm⁻¹ represent vibrations caused by titanium surface groups. The carbon vibrations were represented by the E_g and A_1g peaks at ca. 582/620 cm⁻¹ and ca. 725 cm⁻¹, respectively.^48,49 The broadening and merging of lines in the spectra indicated that the Ti₃AlC₂ precursor had undergone exfoliation and delamination.⁴⁸ The different Raman modes of Ti₃C₂T_x are shown in Fig. 3(d). The vibrations of the free-standing film before and after heat treatment matched the peaks at 123, 198, 247, 286, 382, 582, 620, and 725 cm⁻¹; however, there were some slight variations in the peak intensities. The partial elimination of functional groups was observed upon annealing at a higher temperatures in the range of 350 to 480 cm⁻¹.⁴⁸ Hence, a slight variation in the overall peaks was noted after heat treatment, but the characteristics of the respective functional groups remained the same. It was suggested that some of the OH functional groups had a propensity to transform into oxide (O) increasing the mechanical stability of the membrane and decreasing the d-spacing.⁵⁰ Heat treated and subsequently dried films maintained their chemical stability, allowing them to be stored in an ambient environment (in air) for extended periods of time.

X-ray photoelectron spectroscopy (XPS) was used for determining the surface chemical compositions, atomic bonding, and chemical states of delaminated Ti₃C₂T_x films. Fig. 5(a) shows the survey scan of the M5 free standing thin film, which revealed a series of sharp peaks corresponding to direct excitation of electrons from core levels in Ti, C, O, F, and Cl. The O-KLL and F-KLL peaks were obtained due to Auger electrons and the absence of the Al peak indicated the successful etching of Al during the synthesis process.^32,51,52 Fig. 5(b)–(f) shows high resolution scans of various elements (Ti 2p, C 1s, O 1s, and F 1s) incorporated during exfoliation which were de-convoluted in different peaks using CasaXPS with asymmetric Gaussian–Lorentzian curves. The surface chemistry of Ti₃C₂T_x MXene improved the polarization of local dipoles.⁵³ The systems were also characterized by FTIR spectra and the data for M5 sample are shown in Fig. S5.

Fig. 4(b) shows the high-resolution core level scan of the Ti 2p region, where spin orbit coupling resulted in two peaks with a 2:1 intensity distribution between 2p_3/2 and 2p_1/2 peaks, respectively.⁵⁴ The Ti 2p spectrum was deconvoluted into five peaks, each of which was related to Ti–C (Ti⁺¹), Ti–X (Ti²⁺), Ti–O_y (Ti³⁺) and TiO₂ (Ti⁴⁺). These peaks showed that there were many combinations of terminal groups on Ti₃C₂T_x, corresponding to different oxidation states of Ti. The peak positions and other fitting parameters are given in Table 1, which are consistent with the literature.^{12,30,55–57} Fig. 5(c) shows the C 1s XPS spectrum, which was fitted with five peaks namely Ti–C, C–C, C–O, CO, and –CH_x whose binding energy values are given in Table 1. Fig. 4(d) shows the scan spectrum of F 1s, which was fitted with components corresponding to Ti–F_x and Al–F bonds, with binding energy values shown in Table 1. All peak positions assigned to specific bonds were consistent with the literature.^58–62

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Fig. 4(e) and (f) presents O 1s scans of pristine and heat treated Ti₃C₂T_x thin films. The O 1s spectrum was fitted with five peaks that were attributed to the distinguishing bonds TiO₂, TiO_x, C–OH, and CO. Ti–O_x played a vital role in the stability of the film and prevented its oxidation due to the presence of O_x groups in Ti–O_x that could repel O₂ molecules present in the air. It can be clearly seen that the intensity of the Ti–O_x peak increased, whereas the intensity of C–OH peak decreased for the heat treated Ti₃C₂T_x thin film, indicating the conversion of –OH function groups to oxide (O) groups.⁵⁰ Hence, the presence of more O-related states on the surface of the heat treated Ti₃C₂T_x thin film, compared to the pristine Ti₃C₂T_x thin film, led to higher mechanical stability and oxidation resistance of the former. The XPS results were also consistent with the Raman and XRD results, where the authors noted changes in the functional group region of the Raman spectrum and a forward shift of the (002) diffraction peak, indicating a decrease in d-spacing due to the removal of functional groups.

Fig. 5(a)–(c) shows the FE-SEM micrographs of Ti₃C₂T_x thin films (M5) after exfoliation at three different magnifications. The cross-sectional images of Ti₃C₂T_x thin films confirmed an accordion-like structure, indicating the typical nanosheet morphology after the removal of ‘Al’ between the Ti₃C₂ sheets. The distance between nanosheets was larger due to weak van der Waals interaction among layers and the average thickness of a sheet was about 0.20 μm, whereas the total thickness of the film was 5 μm. The accordion like morphology of Ti₃C₂T_x thin films made the system more favorable for multiple scattering and the brightness of the layers indicated that the film was highly conductive. The highly electrically conductive Ti₃C₂T_x multiple layers formed conductive paths and were arranged in parallel positions, as shown in Fig. 6, which indicated that the system was anisotropic.⁶³ Fig. 5(d)–(f) shows the morphology of the heat treated M5 thin film prepared at 300 °C in an inert environment for four hours. The heat treatment led to significant changes in the layered structure, making it more porous with many interstices, sites, or defects where there would be a high probability of attenuation of EM radiation.

Fig. 5(g)–(i) shows the surface SEM micrographs of fabricated cotton fabric (CF) with a 1.56 mg cm² loading of Ti₃C₂T_x. The micrographs indicated that the coating of Ti₃C₂T_x was uniform with no damage to the weft yarn arrangement of the plain weaving of the cotton fibers. The coating created a conductive path through electrostatic forces, leading to a bright and shiny surface on the fabric as shown in Fig. 5(g)–(i). As cotton fabric dries faster than the layers of deposited Ti₃C₂T_x, this results in the formation of wrinkles on its surface due to compressive stress. The surface of the coated CF was rough and at points of interleaving, the direction of yarn was different, which led to irregularities in the fabric and made the system anisotropic. To study the elemental and chemical composition of Ti₃C₂T_x thin films, EDS measurements were performed (Fig. S4). No ‘Al’ peak was observed in the EDS spectrum of the Ti₃C₂T_x, which confirmed the successful etching of ‘Al’ layers. It is evident from the EDS spectrum that all the expected elements such as Ti, C, and T_x (–OH, –F, –Cl, and –O) were present with atomic ratios given in Table S1. The EDS results could not provide detailed information especially for the –OH group because H cannot be detected by EDS.^37,64 We also observed the presence of Cl functional groups which might play an important role in conducting properties.⁶⁵

Considering the good electrical conductivity of Ti₃C₂T_x thin films, the EMI shielding response of free-standing thin films of various thicknesses was investigated in the frequency range of 8.4 to 12.4 GHz (X-band) as shown in Fig. 6. To study thickness dependent shielding properties, a set of free-standing thin films with different thicknesses named M5 (5 μm thick), M7 (7 μm), M9 (9 μm), and M13 (13 μm) were prepared by the vacuum-assisted filtration method. The variation in different shielding parameters of Ti₃C₂T_x thin films, is shown in Fig. 7(a)–(f) as a function of X-band frequency. The 5 μm-thick film had a maximum SE_T of 45 dB (Table S2), which increased to 60 dB for the 13 μm thick film. SE_A also showed the same trend; it increased with thickness and reached 46 dB for the 13 μm film. SE_A was proportional to the thickness of the shield, which indicated that higher thicknesses led to increased path length, leading to greater attenuation of the electromagnetic waves (eqn (12)). The layered structure of Ti₃C₂T_x thin films as evidenced by FE-SEM images (Fig. 5), was obviously useful for trapping electromagnetic waves as the thickness of the shield increased. The highest SE_T of M13 corresponded to the highest attenuation of 99.999% and an effective absorption of 99.99%, respectively, as shown in Fig. 7(d). The results suggested that the layered structure of Ti₃C₂T_x displayed absorption-dominant phenomena. Moreover, the SE_A part was also prominent due to the presence of functional groups, excess charge carriers, and dipolar polarization, as shown in Fig. 7(a). SE_R hardly changed for all Ti₃C₂T_x films and remained around 9–12 dB, indicating that the difference in SE_T was mostly caused by SE_A; indeed, it is known that SE_R values are mainly determined by impedance mismatches.³ The low value of SE_R also makes this study important as most of the studies in the literature have reported values well above 20 dB.^66,67 Thus, EMI shielding results indicated that the high electrical conductivity, dipolar polarization, and layered structure of the MXene sheets were crucial factors that determined the remarkable EMI shielding performance.

As the shielding properties are strongly related to the layered structure of Ti₃C₂T_x thin films, heat treatment of M5 thin films was performed at 300 °C for four hours in an inert environment of N₂ gas (designated as M5HT). The heat treatment was expected to modify the microstructure of film and tune functional groups. A significant increase of 26 dB was observed in SE_T (71 dB) as shown in Fig. 6(i). The authors observed, as shown in Fig. 6(g), that this increase in SE_T occurred due to enhanced absorption as well as reflection, as evidenced by the high values of SE_A and SE_R. Also, it was noted, as shown in Fig. 5(e) and (f), that the layered structure, and porous nature became more prominent after the heat treatment. This microstructural change was mainly responsible for the significantly high value of SE_A. SE_R also increased from 9 dB to 23 dB, which suggested that along with the microstructural changes, there was also a change in conductivity of the film, which led to increased mismatch and more reflection. This conductivity increase was ascribed to the removal of adsorbed water molecules and surface terminations, leading to a decrease in d-spacing as confirmed by XRD studies. However, the maximum contribution to the total shielding effectiveness was still due to absorption, which is preferable in Ti₃C₂T_x free-standing thin films to avoid secondary pollution. Regardless of film thickness, the EMI SE of all the films studied in this work were well above 20 dB, meeting the requirement for practical commercial applications.

We conducted electrical conductivity measurements on different thin film samples and the outcomes are in alignment with both the flake size and the surface functional groups. As described, the –F terminations tend to improve electron confinement due to the high electronegativity of fluorine, which lowers conductivity. On the other hand, –OH and –O groups improve electron transport, thus enhancing conductivity as shown in Fig. 9(c). Regarding HF-etched samples, the more aggressive etching increases the etch rate of the flakes, which leads to smaller flake sizes (Fig. S2), resulting in greater flake boundary and interface density. This increased boundary density leads to scattering of charge carriers, which decreases conductivity. For the samples that underwent heat treatment, a substantial increase in conductivity was observed. The increases are likely due to be higher ordering of the structure and interflake connections. Increased heat treatment likely increases the interflake contacts and decreases the surface defects, thus improving the charge transport and EMI shielding performance.⁶⁸

Specific shielding effectiveness (SSE) and absolute shielding effectiveness (SSE_T) are key parameters to evaluate the EMI shielding efficiency of Ti₃C₂T_x with different densities and thicknesses. Increases in thickness, density, and mass of films can affect the performance and efficiency of the shielding material. The SSE and SSE_T are given by eqn (13) and (14), respectively, and can be used to perform a comparative analysis of the intrinsic shielding properties of different specimens.

	(13)

	(14)

The calculated values of SSE and SSE_T for M5, M7, M9, and M13 are listed in Table S2 together with their respective thicknesses. The table also shows a literature comparison of these quantities measured on similar systems. The SSE_T for M5 is 55503 dB cm² g⁻¹, which increased to 58121 dB cm² g⁻¹ for the M7 sample. A significant increase in SSE_T was observed for the heat treated M5 sample, where the SSE_T reached 72321 dB cm² g⁻¹. This to the best of our knowledge is the highest value of SSE_T for Ti₃C₂T_x thin films having a thickness of only 5 μm. The high EMI SE of the prepared samples is attributed to the accordion like layered structure of Ti₃C₂T_x (see Fig. 9(b)), which caused multiple internal reflections of incident EM radiation, and its excellent conductivity, which provided abundant free electrons to scatter and absorb the energy of the incident EM radiation. The attached functional groups were responsible for the formation of dipoles (Ti⁺ and OH⁻/F⁻/O⁻/Cl⁻) which were also responsible for the absorption of EM radiation as shown in Fig. 9(a).

Regulating the etching conditions of Al can affect conductivity, stability, and EMI shielding properties of Ti₃C₂T_x thin films. The X-ray diffraction data, EDS spectrum, zeta-sizer results and EMI shielding measurements for films (having different thickness) prepared using HF etched dispersion, are shown in the supplementary information. A comparison of EMI shielding properties of 5 μm films prepared using LiF + HCl (M5) and HF (M5HF) etched dispersions, is shown in Fig. 7. The SE_T for M5HF (5 μm film obtained using HF etched dispersion) was 20 dB, which was significantly smaller than that for the M5 (the one obtained from LiF + HCl treatment) film having the same thickness. It is known that the shielding properties of thin films are strongly dependent on the flake size, conductivity, type of surface terminations and microstructure.⁶⁹ The average flake size of Ti₃C₂T_x nanosheets obtained by minimally intensive layer delamination (MILD) using LiF + HCl as etchants was 615 nm, which reduced to 220 nm in the case of the HF treated system as shown in Fig. S3. The film with large flake size had a large surface area and more surface terminations, which functioned as electric dipoles and provided better connectivity between sheets, leading to much better conductivity, and shielding properties as shown in Fig. 7(a)–(f). The flake size also influenced the stability of dispersions, as smaller sized flakes showed lower stability compared to larger flakes as shown in Fig. S2(a) and (b). According to theoretical studies, the kind and number of surface terminations have a significant influence on the electrical structure and physicochemical properties of MXenes.⁷⁰ It was found that Ti₃C₂T_x films prepared using HF etched dispersion had F as the leading terminations, while films prepared using LiF + HCl etched dispersions contained a larger number of oxide (O) terminations (Table S1). Oxide terminated MXenes are predicted to exhibit higher electrical conductivity compared to F terminated surfaces.⁶⁹ Hence, –OH and –O functional groups contribute to improved electrical conductivity by offering better electron delocalization and interflake coupling, which enhances charge carrier mobility.⁷¹ Also, high –F content as a functional group also decreases interfacial polarization which negatively impacts the EMI shielding response due to a decrease in dielectric loss.¹² These differences in terminal groups have also been observed in the study by Hope et al.⁶⁵ with HF and Li + HCl as etchants. Hence, larger flake sizes led to better conductivity and more functional groups that can induce dielectric loss and lead to good EMI shielding performance in the case of Ti₃C₂T_x thin films prepared using the minimally intensive layer delamination (MILD) method (with LiF + HCl as etchants).¹²

Keeping in view the excellent EMI shielding performance of Ti₃C₂T_x thin films, highly conductive Ti₃C₂T_x coated fabrics were also fabricated. Cotton fabric (CF) was chosen as a substrate to coat the dispersion because the Ti₃C₂T_x is polar in nature and had a negatively charged surface, which adhered well with cellulose (C₆H₅O₁₀)_n-based fabrics (cotton, linen, etc.). The fabric that had been used had high yarn density as well as high porosity. Moreover, the weave pattern of the fabric was ordered in such a way that offered less resistance and supported smooth adhesion of the Ti₃C₂T_x dispersion with the fabric which further increased the conductivity of the coated fabric (Fig. 1(c)). Two samples with 0.8 and 1.6 mg cm⁻² (designated as MX-10 and MX-20, respectively, with loadings of 10 and 20 mg over an area of 12.57 cm²) of Ti₃C₂T_x loading were prepared by using vacuum assisted filtration. Fig. 9 shows the comparison of the shielding parameters of MX-10 and MX-20. SE_T of MX-10 was 50 dB throughout the X-band range of frequency, which increased to 82 dB for MX-20. This increase in SE_T of the MX-20 sample was attributed to high loading of Ti₃C₂T_x nanosheets, providing a more effective material for attenuation. A slight decrease in SE_R and a significant increase in SE_A were observed at MX-20. Both samples showed good attenuation (>99.99%) of the incoming EM radiation which further confirmed that the prepared system can be used for practical applications (>20 dB). Cotton fabric that was used as a substrate also played a key role in the attenuation process. Its porous nature further increased the multiple internal reflections, thus contributing to the attenuation process.^72,73 Moreover, the high yarn density and weave pattern of the fabric were also responsible for high EMI SE, as discussed earlier in the FE-SEM section where we observed that uniform coating of the dispersion led to formation of a conducting network.

The shielding response measurement of both the samples was repeated after 6 months, and the results are shown in Fig. 8(g)–(i). The SE_T of MX-20 fell from 80 dB to 70 dB (reduction of 12.5%) while the SE_T of MX-10 remained the same at ca. 50 dB. These results showed that the samples prepared were suitable for long-term storage and use, making them attractive for practical applications. Excellent designability of fabrics, fabric structure, layers of fabrics, and yarn density are the key features that determine good EMI shielding properties.^74,75 Table S3 shows the calculated value of SE of MX10 and MX20, corresponding to their thickness, along with a literature review. The EMI SE values obtained for the coated fabric are comparable or better than most of the known values in the published work. Finally, a comparison between the shielding parameters of pristine films (under harsh and mild etching condition), heat treated Ti₃C₂T_x thin films and coated fabric, is shown in Fig. 9(c). We conclude that mild etching conditions were suitable for obtaining large flakes, leading to much better and stable Ti₃C₂T_x thin films. Also, temperature had a significant effect on the microstructure and hence, on EMI shielding properties. Moreover, as outlined in Fig. S6, the burning behavior of MXene thin films was studied to assess their flame resistance. The MXene film demonstrates exemplary flame resistance. The findings contribute significantly to the understanding of the correlation of various parameters (etchant type, temperature, flake size, surface chemistry and thickness) in attaining excellent EMI shielding properties, providing opportunities for the development of technologies and devices that mitigate or protect against electromagnetic interference.

Conclusions

In this study, we developed high-performance EMI shielding materials through the rational design of free-standing Ti₃C₂T_x MXene films and functionalized cotton textiles using a scalable vacuum-assisted filtration method. Systematic investigation of etching conditions (LiF + HCl vs. HF), thermal treatment, and thickness effects revealed that a heat-treated 5 μm film achieved a remarkable shielding effectiveness of 71 dB, which is 37% higher than that of untreated films. Moreover, an unprecedented absolute shielding effectiveness (SSE/t) of 72300 dB cm² g⁻¹ was recorded, surpassing all comparable MXene-based shields reported to date. The enhanced performance resulted from thermal conversion of surface terminations (–OH to –O), which improved conductivity while simultaneously creating a porous structure that enhanced wave absorption. Comparative analysis showed that LiF + HCl-etched films (71 dB for 5 μm) significantly outperformed HF-etched counterparts (20 dB for 5 μm) due to larger flake sizes, optimized surface chemistry, and superior electrical conductivity. A 13 μm thick film (untreated) exhibited high shielding of 60 dB, demonstrating thickness-dependent performance tunability.

The practical potential was further evidenced by MXene-coated cotton fabric achieving an excellent shielding effectiveness of ∼82 dB, representing one of the highest values reported for textile-based shields, while maintaining stable performance after six months of ambient exposure. The exceptional performance originated from synergistic effects, including the fabric's porous meta-structure, large flake sizes, optimized surface dipoles (Ti–O, Ti–F, etc.), and high conductivity. These findings provide fundamental insights into the structure–property relationships governing EMI shielding while also establishing a viable manufacturing pathway. The combination of record-breaking performance metrics, environmental stability, and scalable processing positions these MXene-based materials as transformative solutions for next-generation applications in flexible electronics, wearable devices, and aerospace technologies, effectively bridging the gap between scientific innovation and commercial electromagnetic protection needs.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

The data that support the findings of this study are available from the corresponding author, Dr. Shahzad Hussain, upon reasonable request.

Supplementary information is available. See DOI: https://doi.org/10.1039/d5na00662g.

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