Achieving Full Redispersion of Dried MXene Monoliths via Trace Metal Cation Intercalation

Abstract

MXenes, a class of 2D transition metal carbides and nitrides, exhibit exceptional electrical conductivity and solution dispersibility, making them promising materials for various applications. However, their long‐term stability remains a critical challenge due to oxidation in aqueous dispersions. While the transformation of these dispersions into water‐redispersible dry monoliths is highly desirable, achieving this has proven difficult. This study introduces a facile approach to enhance the redispersion yield of dried MXene monoliths by incorporating trace amounts of metal cations (Li⁺, Mg²⁺, and Al³⁺) into aqueous dispersions prior to lyophilization. These cations intercalate between MXene sheets, acting as atomic pillars that inhibit face‐to‐face restacking and facilitate water infiltration during redispersion. Systematic investigations reveal that optimal cation concentrations significantly improve redispersion efficiency without inducing flocculation, achieving yields of up to 100% for Li⁺‐modified MXenes. Characterization of redispersed MXene nanosheets confirms preserved morphology and structural integrity. Furthermore, compared to the pristine MXene counterparts, MXene films made from cation‐aided redispersions show higher electrical conductivity and electromagnetic interference shielding performances. This simple yet effective strategy addresses key challenges in MXene storage and processing, enabling reliable solution‐based fabrication for energy storage, sensing, and electronic applications.

This study presents a simple and highly efficient technique to fully redisperse MXene solid monoliths into aqueous dispersions. By adding trace amounts of metal cations to MXene dispersions prior to drying, complete redispersion of MXene monoliths is achieved.

1. Introduction

MXenes, a class of 2D transition metal carbides, nitrides, and carbonitrides, are characterized by the general formula M_n+1X_nT _x (n = 1, 2, 3, 4).^{[ 1} , ² , ^{3 ]} In this formula, M represents an early transition metal such as titanium (Ti), vanadium (V), molybdenum (Mo), or niobium (Nb); X denotes carbon and/or nitrogen; and T _x refers to surface termination groups like hydroxyl (─OH), oxygen (─O), and fluoride (─F). MXenes have rapidly emerged as versatile materials with exceptional properties, making them highly suitable for various applications, including electromagnetic interference (EMI) shielding,^{[ 4} , ^{5 ]} energy storage,^{[ 6} , ⁷ , ^{8 ]} and sensors.^{[ 9} , ¹⁰ , ^{11 ]} Due to their unique layered structure, MXenes exhibit excellent electrical conductivity, high mechanical strength, large surface area, and tunable surface functionality. Unlike other 2D materials, MXenes offer superior solution dispersibility, attributed to their hydrophilic surface,^{[ 12} , ^{13 ]} which is terminated with functional groups such as ─OH, ─O, and ─F. These features enable MXenes to form stable colloidal solutions in water without additional treatments, allowing them to maintain high electrical conductivity while exhibiting superior solvent dispersibility. This characteristic distinguishes MXenes from other conductive nanomaterials, such as graphene or carbon nanotubes, which often require harsh chemical treatments or surfactants for stable dispersion in solution. Consequently, MXenes are particularly well‐suited for solution‐processable electronic and energy devices.

Despite their exceptional properties, MXenes face significant challenges during long‐term storage in solution form, primarily due to their susceptibility to oxidation.^{[ 14} , ^{15 ]} Oxidation occurs as a result of interactions between MXenes and water molecules or dissolved oxygen in the storage medium. This process not only degrades their electrical conductivity but also compromises their structural integrity and overall performance. To address MXene oxidation in aqueous dispersions, two primary strategies have been explored: reducing the concentration of dissolved oxygen in the storage medium^{[ 16 ]} and introducing antioxidants to chemically neutralize reactive oxygen species.^{[ 17 ]} However, these methods have limited effectiveness, as water itself remains the primary oxidizing agent, leading to the gradual degradation of MXenes. As a result, recent studies have focused on enhancing MXene stability by forming dispersions in organic media, where surface functionalization with organic molecules has emerged as a more effective strategy.^{[ 18} , ^{19 ]} By grafting organic ligands or polymer chains onto MXene surfaces, oxidation resistance can be significantly improved while maintaining stable dispersion in non‐aqueous solvents. Conventional stabilization techniques typically involve covalent or non‐covalent attachment of organic molecules onto MXene sheets, serving as stabilizing agents. While these strategies effectively mitigate chemical oxidation, the presence of these agents can substantially decrease electrical conductivity, limiting their further application.

A more direct and intuitive approach to mitigating oxidation is the complete removal of water, the primary oxidizing agent, by drying MXenes into a solid‐state form. This powdered form not only enhances long‐term stability but also significantly reduces overall weight, making it advantageous for industrial applications, particularly in terms of transportation and storage efficiency. However, this drying process introduces new challenges that negatively impact usability. One critical issue is the restacking of MXene layers during drying, which significantly reduces their accessible surface area and functional properties. This restacking effect severely hinders the redispersion of MXenes into their original aqueous dispersion form, as the tightly stacked layers aggregate and form clumps when reintroduced into solvents. As a result, achieving a uniform dispersion becomes challenging, limiting the applicability of MXenes in solution‐based or printing processes, such as inkjet printing or thin‐film fabrication.

To address these challenges, this work presents a facile approach to significantly enhance the redispersion yield of solid‐state MXene monoliths or powders for efficient long‐term storage. Specifically, by incorporating trace amounts of metal cations into the MXene solution, we effectively inhibit the restacking of MXene sheets during drying and improve their redispersibility in aqueous dispersions. These ionic additives act as atomic pillars intercalated between adjacent MXene sheets, suppressing face‐to‐face restacking and maximizing solution redispersibility. We demonstrate that MXenes modified with trace metal cations exhibit superior dispersion performance compared to pristine MXenes while preserving their intrinsic properties, such as high electrical conductivity. This approach provides a simple yet robust solution to overcome the challenges of MXene storage and redispersion, enabling their reliable application across diverse fields.

2. Results and Discussion

2.1. Introduction of Trace Metal Cations to MXene Dispersions

Figure  1a presents a conceptual schematic comparing conventional and optimized methods for redispersing MXene monoliths. In the conventional approach, MXene aqueous solutions are lyophilized into solid monoliths, typically porous in structure. Lyophilization is preferred over heat‐mediated drying as it preserves a high surface area, facilitating redispersion. Redispersion is achieved by reintroducing water, but its efficiency depends on the extent of van der Waals‐induced restacking of MXene sheets during drying. In the conventional method, restacking occurs readily, restricting water intercalation to structurally irregular sites, thereby limiting redispersion. In contrast, the optimized method developed in this study involves the addition of trace metal cations to the MXene solution before lyophilization. As with the conventional method, the cation‐modified MXenes are freeze‐dried into solid monoliths and later redispersed in water. The added cations intercalate between adjacent MXene sheets through ionic interactions with surface functional groups, acting as atomic “pillars” that increase interlayer spacing. This enhanced spacing facilitates water penetration, improving redispersion efficiency. Also, the presence of hydrophilic metal cations may further enhance water penetration by lowering the kinetic barrier for water intercalation.^{[ 20 ]} Notably, the cation concentration must be carefully controlled, as excessive cations may induce flocculation rather than dispersion.^{[ 21} , ^{22 ]} In this study, Ti₃C₂T _x MXene was selected as the primary material due to its widespread use. It was synthesized from the Ti₃AlC₂ MAX phase via the MILD method,^{[ 2} , ²³ , ^{24 ]} as detailed in the Experimental Section. Figure 1b,c depict the characterization of Ti₃C₂T _x MXene dispersed in water prior to lyophilization. The scanning electron microscopy (SEM) image (Figure 1b) reveals that the typical lateral size of an MXene sheet ranges from 3–5 µm. The transmission electron microscopy (TEM) image and selected area electron diffraction (SAED) pattern (Figure 1c) confirm the successful synthesis of high‐quality single‐layer MXene sheets.^{[ 10} , ^{25 ]} Additionally, UV–vis absorption spectra of as‐synthesized MXene dispersions (Figure 1d) display three characteristic absorption peaks at 260, 320, and 740 nm, consistent with previous reports.^{[ 16 ]}

Figure 1.

a) Schematic illustration of redispersing MXene monoliths using a conventional method (top) and the optimized method developed in this study (bottom). b) SEM image of a single Ti₃C₂T _x MXene sheet on a porous anodized aluminum oxide (AAO) substrate. c) TEM bright‐field image (left) and SAED pattern (right) of a Ti₃C₂T _x sheet. d) UV–vis absorption spectrum of a Ti₃C₂T _x aqueous dispersion.

To systematically investigate the influence of trace metal cations on MXene redispersibility, cations with varying valences were introduced into MXene aqueous dispersions. Lithium (Li⁺), magnesium (Mg²⁺), and aluminum (Al³⁺) were selected as representative monovalent, divalent, and trivalent cations, respectively, each added in the form of their chloride salts. It was hypothesized that cation concentration would play a critical role in determining the redispersion yield, with two key criteria guiding the identification of optimal concentrations.

First, the cation concentration must remain below the threshold at which flocculation occurs, as strong ionic binding between the MXene sheets and cations would hinder redispersion. Second, within this non‐flocculating range, higher cation concentrations are expected to facilitate greater intercalation of water molecules between MXene layers, thereby enhancing redispersion. To experimentally determine the optimal cation concentration, MXene dispersions were prepared with varying concentrations of Li⁺, Mg²⁺, and Al³⁺, as shown in Figure  2a–c. Across all systems, stable dispersions were observed at lower cation concentrations. Specifically, MXenes remained stably dispersed at concentrations below 10⁻² m for Li⁺, and below 10⁻⁴ m for both Mg²⁺ and Al³⁺. Notably, flocculation occurred at significantly lower concentrations for multivalent cations. This behavior is attributed to the stronger electrostatic interactions of multivalent cations with negatively charged MXene surfaces, a phenomenon commonly observed in MXenes and related materials with similar surface chemistries, such as graphene oxide.^{[ 26} , ^{27 ]}

Figure 2.

a–c) Photos of MXene aqueous dispersions upon addition of various concentrations of a) LiCl, b) MgCl₂, and c) AlCl₃. d–f) Zeta potential measurements of MXene aqueous dispersions upon addition of various concentrations of (d) LiCl, (e) MgCl₂, and (f) AlCl₃.

To quantitatively assess the concentration‐dependent dispersion behavior, zeta potential measurements were conducted, as presented in Figure 2d–f. In colloidal systems, dispersions are generally considered stable when the zeta potential magnitude exceeds ±30 mV.^{[ 28 ]} Given that MXenes exhibit negative surface charges under neutral pH conditions, stable dispersions correspond to zeta potential values below –30 mV.^{[ 28} , ^{29 ]} For all cation systems studied, dispersions that remained stable consistently showed zeta potential values below this threshold, comparable to those of pristine MXene aqueous dispersions (Figure S1, Supporting Information). Additionally, as expected, zeta potential magnitudes decreased with increasing cation concentrations, reflecting reduced electrostatic stabilization due to charge screening. Based on these experimental findings, the optimal cation concentrations for achieving maximum redispersion without inducing flocculation were determined to be 10⁻² m for Li⁺ and 10⁻⁴ m for both Mg²⁺ and Al³⁺ _.

2.2. Redispersion Yield of MXene‐Cation Complexes

MXene dispersions containing optimal concentrations of cations were lyophilized to form monoliths of MXene‐cation complexes for redispersion studies. MXenes combined with trace amounts of Li⁺, Mg²⁺, and Al³⁺ were hereafter referred to as T‐LiMX, T‐MgMX, and T‐AlMX, respectively. Figure  3a illustrates the expected stacking structure post‐lyophilization, where cations are sparsely intercalated between adjacent MXene sheets, bound to surface functional groups via ionic interactions. X‐ray photoelectron spectroscopy (XPS) in Figure S2 (Supporting Information) shows the high‐resolution Li 1s, Mg 1s, and Al 2p spectra for T‐LiMX, T‐MgMX, and T‐AlMX, respectively. For all samples, deconvoluted peaks were centered at positions allocated to metal hydroxides and metal fluorides, which indicate that the metal cations are indeed bonded to the –OH and –F surface functional groups of MXene. We note that for T‐MgMX and T‐AlMX, samples synthesized using higher ion concentrations (10⁻³ m) were utilized, as the very low ion concentration in optimized conditions could not be reliably detected. We speculate that this change in concentration will not majorly influence the main chemical bonding nature between the MXene surface and the metal cation.

Figure 3.

a) Schematic illustration of the MXene interlayer structures in a lyophilized MXene‐cation complex. b) SEM images and photos (insets) of lyophilized T‐LiMX, T‐MgMX, and T‐AlMX. c) Schematic illustration of the molecular structures in a redispersed MXene solution. d,e) Photos of redispersed T‐LiMX, T‐MgMX, and T‐AlMX dispersions at (d) relatively concentrated and (e) relatively dilute concentrations. f) UV–vis absorption spectra of redispersed solutions. g) Enlarged UV–vis absorption spectra near the 700–800 region and the MXene concentration derived from peak intensities. h) Calculated redispersion yields.

Figure 3b presents SEM images and photographs of the lyophilized MXene‐cation complexes. All three samples exhibited porous monolithic structures, with SEM images revealing that MXene sheets assembled into random 3D networks, a typical outcome of lyophilization. For comparison, lyophilized pristine MXene monoliths referred to as PMX, were synthesized as a control. Similar to the MXene‐cation complexes, PMX displayed porous structures, with SEM images confirming 3D sheet assembly (Figure S3, Supporting Information).

To assess redispersion behavior, deionized water was added to the lyophilized monoliths, followed by mild agitation to facilitate sheet delamination, as schematically shown in Figures 3c,d shows photographs of the redispersed T‐LiMX, T‐MgMX, and T‐AlMX dispersions, all of which exhibited uniform, stable dispersions without visible aggregation. The diluted dispersions displayed a characteristic greenish hue (Figure 3e), indicative of well‐dispersed Ti₃C₂T _x sheets. The redispersion yield was quantified by comparing the MXene concentration in the initial and redispersed solutions, following the equation:

$$\mathrm{Redispersion}\mathrm{yield}\left(\%\right)=\frac{C_{\mathrm{MXene}\left(\mathrm{redispersion}\right)}}{C_{\mathrm{MXene}\left(\mathrm{initial}\mathrm{dispersion}\right)}}\times 100\%$$ (1)

The concentration of each dispersion was determined via UV‐vis absorption spectroscopy. For an accurate comparison, equal masses of MXene were used to prepare PMX, T‐LiMX, T‐MgMX, and T‐AlMX monoliths, which were redispersed in identical volumes of water to achieve a target concentration of 1 mg mL⁻¹. Figure 3f displays the UV–vis spectra of the redispersed PMX, T‐LiMX, T‐MgMX, and T‐AlMX samples. The spectral profiles closely matched that of the initial MXene dispersion (Figure 1d), featuring two characteristic peaks. In the UV region (region i), the higher intensity of the 320 nm peak relative to the 260 nm peak suggests that the MXene sheets remained intact and unoxidized during lyophilization and redispersion.^{[ 30 ]} In the visible region (region ii), a distinct peak was observed at 730–750 nm, which was used to calculate the redispersion yield. Given the linear relationship between peak absorbance in region ii and MXene concentration,^{[ 31 ]} the redispersion concentrations of PMX, T‐LiMX, T‐MgMX, and T‐AlMX were determined (Figure 3g). Applying Equation (1), the redispersion yields were calculated (Figure 3h). Remarkably, T‐LiMX exhibited a redispersion yield near 100%, indicating nearly complete recovery of the lyophilized MXene. T‐MgMX and T‐AlMX also showed high yields of 92% and 94%, respectively. In contrast, PMX demonstrated a significantly lower redispersion yield of 70%, reflecting a 30% dispersion loss during the lyophilization‐redispersion process. These results clearly demonstrate the superior redispersibility of MXene‐cation complexes. To evaluate the influence of monolith storing period on the redispersion yield, PMX, T‐LiMX, T‐MgMX, and T‐AlMX monoliths were redispersed after 15 days of storage, and the redispersion behavior was investigated through UV‐vis spectroscopy (Figure S4, Supporting Information). The results demonstrated that T‐LiMX maintained 100% redispersion efficiency even after 15 days of storage, while PMA, T‐MgMX, and T‐AlMX showed 53%, 67%, and 84% redispersion yields, respectively, demonstrating degraded efficiency. These findings indicate that T‐LiMX exhibits superior long‐term redispersion stability compared to other cation‐modified MXenes.

The redispersion yield was influenced by the initial cation concentration prior to lyophilization. As shown in Figures S5 and S6 (Supporting Information), samples with cation concentrations exceeding the optimized conditions exhibited lower redispersion yields. This reduction is attributed to stronger inter‐sheet attractions at higher cation concentrations, which impede effective delamination upon water addition. Also, the influence of initial MXene concentration on redispersion efficiency was further evaluated. To evaluate this effect, optimal concentrations of Li⁺ were added to MXene dispersions with initial concentrations of 0.5 and 2.0 mg mL⁻¹, then lyophilized into monoliths and redispersed in water. Then, UV–vis spectroscopy was performed to assess the redispersion yield, as shown in Figure S7 (Supporting Information). While the redispersion yields were slightly lower compared to that observed in Figure 3h, all samples showed a redispersion yield near 100%.

2.3. Properties and Quality of Redispersed MXene Nanosheets

The quality and properties of MXene sheets in the redispersions of T‐LiMX, T‐MgMX, and T‐AlMX were further analyzed. Figure  4a presents SEM images of individual MXene sheets from each redispersion. The lateral size of the sheets was measured to be approximately 3 to 5 µm, indicating that the freeze‐drying and redispersion process did not significantly alter their structure. Atomic force microscopy (AFM) measurements were also conducted to determine the thickness of individual sheets inside the dispersion (Figure S8, Supporting Information). For both the original MXene dispersion and the redispersion (T‐LiMX), the thickness of a MXene sheet was between 1.5 and 2 nm, indicating that MXene sheets were well delaminated down to single‐layer sheets, confirming the excellent redispersion capability. XPS analyses were further performed to assess the chemical state of redispersed MXene sheets. The Ti 2p spectra of the original Ti₃C₂T _x MXene, T‐LiMX, T‐MgMX, and T‐AlMX all similarly show a very low intensity of the TiO₂ peak centered at 458.5 eV, showing that chemical oxidation did not occur during the entire process (Figure S9, Supporting Information). In overall, the structural morphology and chemical states closely resembled those in the original dispersion, indicating that the sheets remained undamaged during the redispersion process.

Figure 4.

a) SEM images of a single T‐LiMX, T‐MgMX, and T‐AlMX sheet on porous anodized aluminum oxide (AAO) substrates. b) XRD analyses of MXene films. c,d) d‐spacing (c) and FWHM values (d) derived from the (002) peaks in (b). e) EMI SE values of PMX, T‐LiMX, T‐MgMX, and T‐AlMX films at the X‐band.

Elemental analyses (EDS) and XPS were also conducted to evaluate the presence of residual metal cations in T‐LiMX, T‐MgMX, and T‐AlMX films. XPS results showed that the atomic percentage of Li⁺ in the optimized T‐LiMX sample was ≈0.03%. On the other hand, Mg²⁺ and Al³⁺ were not detected, neither in EDS (Figure S10, Supporting Information) nor the XPS analyses for the T‐MgMX and T‐AlMX samples, respectively. Given that the atomic detection limit of XPS is ≈0.01%, this suggests that the residual concentrations of Mg²⁺ and Al³⁺ are below this threshold, likely due to the addition of a very low ion concentration of 10⁻⁴ m for both ions. These trace levels are expected to have negligible effects on the electrical properties of the MXene films. However, the presence of residual cations was detectable via X‐ray diffraction (XRD) measurements. The XRD patterns of T‐LiMX, T‐MgMX, and T‐AlMX films exhibited a strong (002) peak, similar to that observed in pristine MXene films (Figure 4b). The calculated interlayer spacing (d‐spacing) for T‐LiMX, T‐MgMX, and T‐AlMX films was ≈1.44 nm, slightly larger than the 1.38 nm observed for pristine MXene films (Figure 4c). Additionally, the full‐width at half‐maximum (FWHM) of the (002) peak was broader for T‐LiMX, T‐MgMX, and T‐AlMX films, ranging between 0.6° and 0.8°, compared to 0.44° for pristine MXene (Figure 4d). These slight increases in d‐spacing and FWHM suggest the presence of trace residual cations, which likely act as interlayer spacers, subtly modifying the film structure.

Given the high electrical conductivity and lightweight nature of MXene films, their application in EMI shielding has been extensively studied.^{[ 4} , ³² , ³³ , ^{34 ]} To further evaluate the redispersed MXenes, we measured and compared the EMI shielding performance of films assembled from T‐LiMX, T‐MgMX, and T‐AlMX dispersions. Figure 4e displays the EMI shielding effectiveness (SE) of these films within the X‐band frequency range (8–12 GHz). The total shielding effectiveness (SE_T) values for PMX, T‐LiMX, T‐MgMX, and T‐AlMX films were measured at 47.4, 59.8, 46.9, and 46.8 dB, respectively. Among these, T‐LiMX exhibited the highest SE_T, surpassing even the PMX film. This superior performance can be attributed to the higher electrical conductivity of T‐LiMX films, as confirmed by four‐point probe measurements (Figure S11, Supporting Information). Films derived from dispersions with poor redispersion yields, such as PMX, likely contain restacked MXene particles that hinder the formation of uniform laminated structures. These structural irregularities introduce regions of high contact resistance, ultimately degrading overall electrical conductivity. Across all samples, the absorption shielding effectiveness (SE_A) consistently exceeded the reflection shielding effectiveness (SE_R), with similar SE_A‐to‐SE_R ratios observed in each case. This consistency suggests that the EMI shielding mechanism remains unchanged among PMX, T‐LiMX, T‐MgMX, and T‐AlMX films, likely due to their structural similarities.

3. Conclusion

In this study, we developed and systematically investigated an optimized approach to enhance the redispersibility of Ti₃C₂T _x MXene monoliths through the introduction of trace metal cations prior to lyophilization. By intercalating monovalent (Li⁺), divalent (Mg²⁺), and trivalent (Al³⁺) cations into MXene aqueous dispersions, we demonstrated a significant improvement in redispersion yields compared to conventional methods. The cations acted as atomic “pillars,” increasing interlayer spacing and facilitating water intercalation upon redispersion. Optimal cation concentrations, 10⁻² m for Li⁺ and 10⁻⁴ m for Mg²⁺ and Al³⁺, were determined to maximize redispersion without inducing flocculation. Redispersion yields approached near‐complete recovery, with T‐LiMX achieving ≈100%, and T‐MgMX and T‐AlMX yielding 92% and 94%, respectively. In contrast, pristine MXene monoliths (PMX) exhibited a significantly lower yield of 70%, highlighting the efficacy of the cation‐assisted approach. Characterization of the redispersed MXene sheets confirmed the preservation of their structural integrity and single‐layer morphology. Additionally, films fabricated from the redispersed MXenes showed slight increases in interlayer spacing due to residual cations, though these had negligible effects on the films' electrical properties. Importantly, the enhanced redispersion translated to improved EMI shielding performance, particularly for T‐LiMX films, which exhibited the highest shielding effectiveness (59.8 dB) and electrical conductivity among all samples. These findings demonstrate the potential of cation‐assisted lyophilization as a scalable and effective strategy for producing high‐quality, redispersible MXene powders suitable for advanced applications in energy storage, electronics, and EMI shielding.

4. Experimental Section

Materials

To synthesize the Ti₃AlC₂ MAX phase, TiC (99.9%, −250 mesh, Alfa Aesar), Ti (99.5%, −325 mesh, Alfa Aesar), and Al (99.5%, −325 mesh, Alfa Aesar) were used. To synthesize the Ti₃C₂T _x MXene, lithium fluoride (98.5%, Alfa Aesar) and hydrochloric acid (37%, Daejung Chemical) were used. To synthesize the Ti₃C₂T _x MXene‐cation complexes, LiCl (99.98%, Sigma‐Aldrich), MgCl₂ (99.9%, Sigma‐Aldrich), and AlCl₃ (98%, Sigma‐Aldrich) were used.

Synthesis of Ti₃AlC₂ MAX Phase

Titanium carbide (TiC), titanium (Ti), and aluminum (Al) powders were mixed in an atomic ratio of 2:1:1. The powder mixture was subjected to ball milling at 100 rpm for 6 hours using zirconia balls. The milled powders were then placed into an alumina boat, which was subsequently loaded into a tube furnace. To maintain an inert atmosphere, the furnace was purged with Ar gas at a flow rate of 500 cc/min for 2 hours. The furnace was then heated to 1400 °C at a heating rate of 5 °C min⁻¹, held at the target temperature for 2 hours, and cooled to room temperature at a controlled cooling rate of 5 °C min⁻¹. After cooling, the synthesized Ti₃AlC₂ was obtained in shape of a bar, which was then ground into a fine powder using a drill machine. The resulting powders were further sieved using a 325‐mesh sieve to ensure uniform particle size for subsequent applications.

Synthesis of Ti₃C₂T_x MXene

MXene was synthesized using the MILD (Minimally Intensive Layer Delamination) method, involving the selective etching of aluminum from the MAX precursor. The resulting multilayer MXene is then delaminated through gentle hand‐shaking facilitated by the presence of water and Li ions between the MXene layers. First, 1.6 g of LiF was added to a 20 mL solution of 9 M HCl in a polypropylene (PP) bottle. The mixture was stirred at 360 rpm at 35 °C for 5 minutes. Once the LiF powders completely dissolved in the HCl solution, 1 g of Ti₃AlC₂ powder was slowly added to the solution while stirring, and the reaction continued at 35 °C for 24 hours. After 24 hours, when the reaction was completed, the mixture was centrifuged at 3500 rpm for 5 minutes, and the supernatant was then removed. Deionized (DI) water was added to the conical tube and hand‐shaking was performed to disperse the sediment completely in water. This procedure was repeated until the pH of the supernatant approached 6. When the pH reached ≈6, DI water was added and vigorously shaken for 20 minutes to delaminate the multi‐layered MXene. To eliminate the unreacted MAX and multilayered MXene, the solution was centrifuged at 3500 rpm for 30 minutes, and the supernatant containing the single layer was extracted.

Trace Cation Addition and Lyophilization

For the preparation of Ti₃C₂T _x MXene‐cation complexes, Ti₃C₂T _x solutions of 0.5, 1.0, and 2.0 mg mL⁻¹ concentration were mixed with either LiCl, MgCl₂, or AlCl₃ solutions of various concentrations in a 10 mL vial. The mixtures were then stirred at room temperature for 1 hour. To ensure uniform intercalation of the metal cations, the MXene sheets were well‐dispersed in the solution before introducing the metal cations. The cations were added in precise amounts, followed by mild stirring to facilitate homogeneous interaction with the MXene surface and interlayer space. Additionally, ultrasonic treatment was applied to further enhance dispersion and promote uniform intercalation while preventing agglomeration or excessive clustering. After these steps, the solutions were lyophilized at ‐110 °C to obtain MXene‐cation monoliths.

EMI Shielding Measurements

The electromagnetic interference (EMI) shielding properties of the samples were evaluated using an advanced ultra‐frequency device designed for analyzing dielectric and optical characteristics, specifically a vector network analyzer (VNA, N5222B, Keysight, USA). Measurements were conducted utilizing a rectangular waveguide fixture, covering the X‐band frequency range (8.0–12 GHz). The VNA provided S‐parameters, which were subsequently used to calculate the EMI shielding effectiveness (SE) using the following equations:

$$S{E}_{\mathrm{R}}=10\log \left(\frac{1}{1-{\left|S_{11}\right|}^2}\right)$$ (2)

$$S{E}_{\mathrm{A}}=10\log \left(\frac{1-{\left|S_{11}\right|}^2}{{\left|S_{21}\right|}^2}\right)$$ (3)

$$S{E}_{\mathrm{T}}=S{E}_{\mathrm{R}}+S{E}_{\mathrm{A}}$$ (4)

Characterization

The surface morphologies of Ti₃C₂T _x MXene sheets were observed using scanning electron microscopy (SEM, Regulus 8230, Hitachi) and transmission electron microscopy (TEM, Tecnai F20, FEI). X‐ray diffraction (XRD) patterns were obtained using films XRD system (XRD, Dmax2500‐PC, Rigaku, Japan), Cu Kα radiation (40 kV, 200 mA, λ = 1.5406 Å) in the 2θ range of 3–40° with a scanning step of 0.02° and a scan speed of 2°/min. The chemical structures were analyzed by X‐ray photoelectron spectroscopy (XPS, PHI 5000 Versaprobe, Ulvac‐PH, Japan).

Conflict of Interest

The authors declare no conflict of interest.

Supporting information

Supporting Information

Lee J., Cho S. H., Jang J. M., Woo S. H., Kang Y. C., and Kim S. J., “Achieving Full Redispersion of Dried MXene Monoliths via Trace Metal Cation Intercalation.” Small Methods 9, no. 9 (2025): 2500383. 10.1002/smtd.202500383

Data Availability Statement

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