Two-dimensional (2D) materials have been a hot topic ever since graphene was first isolated. Among them, MXenes are one of the fastest-growing families thanks to their combination of high electrical conductivity, tunable chemistry, and solution processability.

This blog focuses on one particular MXene: titanium carbide, Ti₃C₂Tₓ, which is currently the most widely studied member of the MXene family. The original article you shared is a detailed methods paper explaining how to synthesize and process Ti₃C₂Tₓ step by step. Here, we’ll translate that into a clear, simple, and logical blog post—no confusing jumps, no assumptions about figures you can’t see, and no imaginary data.

We’ll walk through:

• What MXenes and MAX phases are

• How Ti₃C₂Tₓ is made from Ti₃AlC₂

• Different etching routes (HF and “in situ” HF)

• How delamination and intercalation work

• How to turn MXene into inks and films

• How to store and characterize it

• Which synthesis route to choose for different applications

1. What Are MXenes and Where Does Ti₃C₂Tₓ Fit In?

MXenes are a family of 2D materials made from transition metal carbides, nitrides, or carbonitrides. Their general formula is:

Mₙ₊₁XₙTₓ

• M = early transition metal (Ti, V, Nb, Mo, etc.)

• X = carbon and/or nitrogen

• Tₓ = surface terminations such as –O, –OH, –F that come from the etching solution

They are produced by selectively removing one element (called “A”) from layered precursors called MAX phases.

A MAX phase has the formula:

Mₙ₊₁AXₙ

• A = elements from group 13–14 (e.g. Al, Si)

For Ti₃C₂Tₓ MXene, the parent MAX phase is Ti₃AlC₂. When the aluminum (Al) layers are chemically removed, the remaining structure is Ti₃C₂, with surface terminations (Tₓ) coming from the etchant.

MXenes are attractive because they combine:

• Metal-like electrical conductivity

• Hydrophilic surfaces (they disperse in water)

• Tunable interlayer spacing and chemistry

• Compatibility with solution processing (coatings, inks, films, membranes)

Ti₃C₂Tₓ in particular is heavily studied in:

• Energy storage (supercapacitors, batteries)

• Electromagnetic interference (EMI) shielding

• Water purification

• Catalysis

• Conductive films and coatings

Because of this, how you synthesize and process Ti₃C₂Tₓ directly affects its performance—flake size, defects, surface chemistry, conductivity, and stability all depend on the route you choose.

2. From MAX to MXene: The Core Idea

The basic transformation is:

Ti₃AlC₂ (MAX) → Ti₃C₂Tₓ (MXene)

To achieve this, you need to selectively dissolve the Al layers without destroying the Ti–C backbone. This is done by wet chemical etching, usually with:

• Direct hydrofluoric acid (HF)

• Or solutions that generate HF in situ (inside the solution) from fluoride salts plus a strong acid

After etching, the stacked Ti₃C₂ layers remain, but they are still tightly packed. To obtain single or few-layer flakes, you then:

1. Wash away acids and by-products

2. Often intercalate larger ions or molecules between the layers

3. Delaminate—separate the layers into individual flakes, with or without sonication

These steps control:

• Flake size (hundreds of nanometers vs several micrometers)

• Defect density

• Type and amount of surface terminations

• Electrical and mechanical properties

The paper you shared doesn’t just say “here is one method”—it compares multiple etching and delamination strategies and explains their pros and cons.

3. Etching with HF: Concentration Matters

One widely used approach is direct etching of Ti₃AlC₂ with HF. The authors investigated three HF concentrations:

• 30 wt% HF

• 10 wt% HF

• 5 wt% HF

In all cases, they used the same general procedure:

1. Slowly add Ti₃AlC₂ powder into HF under stirring

2. Let the reaction proceed at room temperature for a set time (hours)

3. Wash repeatedly with deionized water by centrifugation until the supernatant pH is around 6

4. Collect the sediment and dry it in vacuum to obtain Ti₃C₂Tₓ powder

Key point: Even low HF concentration (5 wt%) is enough to remove the Al and form Ti₃C₂Tₓ—just with longer etching time.

3.1 Morphology: The “Accordion-Like” Look

At higher HF concentrations (e.g. 30 wt%), the etched powders often show a characteristic “accordion-like” morphology, where the layers appear more opened up. This is linked to:

• Stronger reaction

• More gas (H₂) evolution during etching

• Greater expansion of the layered structure

At lower HF (e.g. 5 wt%):

• The structure looks much closer to the original dense MAX phase when you only look visually

• But X-ray diffraction (XRD) and elemental analysis (EDX) confirm that Al is still removed and Ti₃C₂Tₓ is indeed formed

Important takeaway:
You cannot judge etching success just by whether it “looks like an accordion” in images. XRD and composition analysis are essential to confirm that Al is gone and the MXene phase is present.

4. Safer Alternatives: “In Situ” HF Formation

Because HF is hazardous, many groups prefer to generate HF inside the solution using fluoride salts and strong acids. Two main “in situ HF” strategies discussed are:

1. Ammonium bifluoride (NH₄HF₂)

2. Lithium fluoride (LiF) + hydrochloric acid (HCl)

4.1 NH₄HF₂-Based Etching

With NH₄HF₂, the etching still follows the same logic: selective removal of Al from Ti₃AlC₂. The process:

• Mix Ti₃AlC₂ powder with an aqueous NH₄HF₂ solution

• Let the reaction proceed (e.g. 24 hours at room temperature)

• Wash and filter as in the HF route

• Dry the resulting powder

The resulting multilayered Ti₃C₂Tₓ:

• Does not usually show a dramatic accordion expansion

• Still shows the removal of Al in XRD patterns (no residual Ti₃AlC₂ peaks)

• Has larger interlayer spacing (d-spacing) due to intercalated NH₄⁺ and water molecules

These intercalated species affect both structure and later delamination behavior.

4.2 LiF/HCl: Clay and MILD Methods

The second in situ HF strategy uses LiF + HCl. This has led to two distinct protocols:

• A “clay” method (earlier, lower LiF content)

• A more optimized MILD method (Minimally Intensive Layer Delamination)

The chemical idea:

• LiF reacts with HCl to create HF in solution

• At the same time, Li⁺ ions become available and can intercalate between MXene layers

The exact concentrations of LiF and HCl are crucial. The paper explains that:

• Higher LiF:Ti₃AlC₂ ratios and stronger HCl (e.g. 9 M) help produce larger, higher-quality Ti₃C₂Tₓ flakes

• In the optimized MILD method, they use relatively high LiF and HCl, and room-temperature etching for about 24 hours

One interesting observation during washing:

• After several centrifugation cycles and adjusting pH, the sediment at the bottom of the tube swells and splits into:

  • A black, clay-like Ti₃C₂Tₓ-rich layer

  • A gray layer containing a mixture of unetched MAX and MXene

The authors carefully separate the black Ti₃C₂Tₓ “slurry” from the gray residue. The black fraction can be:

• Filtered to form free-standing films

• Redispersed in water to form stable colloidal suspensions

These MILD-derived MXenes:

• Contain larger, less defective flakes, often several micrometers wide

• Exhibit very high electrical conductivity when made into films (around 6000–8000 S/cm)

Because of that, the authors strongly favor the MILD route for applications where large flakes and high conductivity are critical.

5. Intercalation and Delamination: Turning Powders into 2D Flakes

Once you have multilayered Ti₃C₂Tₓ powder, the next challenge is to separate the stacked layers into single- or few-layer flakes. This usually involves:

1. Introducing intercalants between the layers

2. Providing some mechanical energy (stirring or sonication)

3. Separating the flakes by centrifugation

5.1 Why Intercalation?

In multilayer MXene, layers are held together by:

• Hydrogen bonding

• Van der Waals forces

• Electrostatic interactions

If you insert larger ions or molecules between these layers, you weaken the attraction and expand the spacing. That makes it much easier to peel the layers apart and obtain well-dispersed 2D flakes in solution.

5.2 DMSO: Early Organic Intercalant

One of the first intercalants used was dimethyl sulfoxide (DMSO):

• MXene powder is mixed with DMSO

• Intercalation occurs

• Sonication is needed to help separate the layers

The result is a colloidal solution of relatively small flakes (typically a few hundred nanometers in size). Without sonication, the material tends to sediment and not remain well-dispersed.

5.3 TMAOH and TBAOH: Tetraalkylammonium Intercalants

The paper also discusses tetramethylammonium hydroxide (TMAOH) and tetrabutylammonium hydroxide (TBAOH):

• These contain bulky organic cations (TMA⁺, TBA⁺) that can replace protons and intercalate between MXene layers

• For Ti₃C₂Tₓ made by HF or NH₄HF₂ etching, TMAOH intercalation followed by washing and centrifugation leads to stable aqueous colloids

• The typical flake size after such processing is around 0.2–0.7 μm (hundreds of nanometers)

XRD measurements show that the basal plane peak (related to layer spacing) shifts to lower angles, indicating increased interlayer distance due to TMA⁺ intercalation.

However, there is an important trade-off:

• Strong stirring and sonication with these organic bases can fragment flakes and introduce more defects

• That reduces flake size and can lower film conductivity

TBAOH is similar but larger; the authors note that longer stirring times are required to achieve effective intercalation and delamination.

5.4 Lithium-Ion Intercalation in the MILD Method

In the MILD LiF/HCl method, the intercalant is Li⁺, formed during etching. There are two big advantages:

1. No sonication is required to delaminate—manual shaking is often enough

2. Flakes remain larger and less damaged

After appropriate washing and pH adjustment:

• A stable, dark-green Ti₃C₂Tₓ colloidal solution forms

• Centrifugation can be used to adjust flake size distributions

• Typical concentrations are around 1–2 mg/mL, higher than many TMAOH-based dispersions

When the authors compare MILD-Ti₃C₂Tₓ flakes with TMAOH-delaminated flakes under electron microscopy:

• MILD flakes are bigger, often >2 μm, with clean, straight edges

• TMAOH-treated flakes are smaller, more irregular, and show more signs of fragmentation

Overall, MILD + Li⁺ intercalation is the method of choice when you want:

• Large flakes

• Fewer structural defects

• High film conductivity and good mechanical properties

6. Processing MXene into Films, Coatings, and Inks

Once you have a colloidal dispersion of Ti₃C₂Tₓ, you can treat it like an ink or paint. The article describes several practical routes for shaping MXene into functional structures.

6.1 Controlling Flake Size: Sonication and Centrifugation

Flake size can be tuned in two main ways:

• Sonication (bath or tip)

  • Longer or more powerful sonication → smaller flakes, more defects

  • Overheating must be avoided to limit oxidation (cooling, ice bath, and inert gas bubbling help)

• Centrifugation

  • Low speeds / short times → larger flakes remain in supernatant, very large ones sediment

  • Higher speeds → progressively remove larger flakes, leaving primarily smaller flakes suspended

By combining these tools, it’s possible to prepare size-selected fractions for different applications.

6.2 Deposition Methods

Some common ways to make MXene structures are:

1. Vacuum-assisted filtration

   • Colloidal MXene is filtered through a porous membrane

   • The flakes accumulate to form a freestanding film

   • The film can be peeled off, used as an electrode or EMI shield, or combined with other materials

2. Spin coating

   • A droplet of MXene dispersion is placed on a substrate (e.g., glass, silicon)

   • The substrate is spun at high speed

   • A thin, uniform film forms—useful for transparent conductors or electronics

3. Spray coating

   • MXene “ink” is sprayed onto substrates (plastics, textiles, large-area surfaces)

   • Suitable for flexible shielding, antennas, or large-scale coatings

   • Films are often rougher than spin-coated ones, but scalable and versatile

4. Rolling, painting, printing

   • If the dispersion is concentrated, it can behave like a clay or paste

   • It can be rolled into thick films or painted onto substrates

   • Screen printing or inkjet printing can pattern MXene for devices

Because MXenes are hydrophilic and negatively charged, substrate preparation matters. Surface treatments (e.g. oxygen plasma, UV/ozone, or chemical cleaning) are often used to make substrates more hydrophilic and improve film uniformity and adhesion.

7. Storage: How to Keep MXene from Degrading

A key practical issue with Ti₃C₂Tₓ is that it oxidizes over time, especially in water and in the presence of dissolved oxygen, heat, and light. Oxidation eventually leads to formation of titanium oxide (TiO₂) and loss of MXene properties.

The paper suggests several strategies:

• Store aqueous MXene dispersions in sealed vials under inert gas (e.g. argon)

• Keep them refrigerated to slow down reactions and avoid light exposure

• Monitor changes in the solution using UV–vis spectroscopy (peak intensity decreases as oxidation progresses)

• For long-term storage, consider:

  • Dispersing MXene in certain organic solvents that better stabilize the flakes

  • Filtering and drying MXene into a film, then redispersing it later if needed

However, drying at too high temperature can make layers bond strongly and hurt later redispersion.

8. Characterization: Checking Quality and Phase

To make sure you have the material you think you have, and that your synthesis route is giving reproducible results, several tools are used:

• X-ray diffraction (XRD)

  • Confirms that the MAX phase has been transformed into MXene

  • Shows disappearance of Ti₃AlC₂ peaks and appearance/shift of Ti₃C₂Tₓ basal peaks (e.g. (002))

• Scanning electron microscopy (SEM)

  • Reveals particle morphology (compact MAX vs etched MXene vs “accordion-like” structure)

  • Gives a visual impression of flake size and packing

• Energy-dispersive X-ray spectroscopy (EDX)

  • Confirms removal of aluminum and presence of Ti, C, and surface elements (O, F, etc.)

• Dynamic light scattering (DLS)

  • Estimates the size distribution of MXene flakes in colloidal solutions

• Four-point-probe electrical measurements

  • Measure conductivity of MXene films

  • In this study, films from MILD Ti₃C₂Tₓ reach around 8000 S/cm, while films from TMAOH-delaminated MXene are much less conductive (around 200 S/cm), illustrating how synthesis and processing routes directly impact performance.

The idea is that no single measurement is enough. Combining structural, compositional, and functional measurements gives a reliable picture of the material.

9. Which Method Should You Use?

The central message of the paper is not “this is the only correct way”, but “different synthesis routes create different kinds of Ti₃C₂Tₓ, and you should choose based on your application”.

If you need:

• High electrical conductivity

• Large flakes (micron-sized)

• Low defect density

• Good mechanical properties

→ The MILD LiF/HCl method is strongly recommended.

If you want:

• Smaller flakes

• Higher edge density or defects (useful in some catalysis or certain electrochemical reactions)

• Or you already have HF-based infrastructure

→ HF-etched or “clay” LiF/HCl methods using sonication and small organic intercalants (e.g. DMSO, TMAOH) may be more suitable.

The key point is that Ti₃C₂Tₓ is not a single fixed material. Its properties are strongly shaped by:

• The etchant (HF vs NH₄HF₂ vs LiF/HCl)

• The concentrations and etching times

• The intercalants used (Li⁺, TMA⁺, DMSO, etc.)

• How aggressively it’s shaken or sonicated

• How the material is stored and handled

By understanding how each step affects the final MXene, researchers and engineers can choose protocols that match their target application rather than using a one-size-fits-all recipe.

10. Final Thoughts

This methods paper on Ti₃C₂Tₓ MXene is essentially a practical handbook for anyone working with or entering the MXene field. It:

• Shows that low HF concentrations and in situ HF methods can safely and effectively produce Ti₃C₂Tₓ

• Introduces the MILD route as a powerful way to get large, high-quality flakes without harsh sonication

• Explains how to intercalate, delaminate, process, deposit, and store MXene in a reproducible way

• Emphasizes that synthesis details are not cosmetic—they directly control performance

For anyone planning to use Ti₃C₂Tₓ MXene in batteries, supercapacitors, EMI shielding, membranes, or electronics, this understanding is crucial. The “same” Ti₃C₂Tₓ from different labs may behave very differently if produced via different routes.