pH-programmed MXene treatment changes PET textile interface

A recent laboratory study has demonstrated that altering the pH of the treatment environment can significantly impact the surface chemistry and performance of PET textiles functionalized with Ti3C2Tx MXene. Researchers explored the effects of neutral water, mildly acidic ascorbic acid, and strongly alkaline sodium hydroxide solutions, maintaining a consistent MXene concentration of 10% relative to fabric weight.

The study involved treating plain-woven PET fabric with an areal density of 88 g/m² at 100 °C for 60 minutes, followed by washing, drying, and heat-fixing at 210 °C for 15 minutes. The pH values of the treatment baths were approximately 6.5–7.0, 4.5–5.0, and 12.5. Ti3C2Tx MXene with a purity exceeding 98% was utilized in this controlled materials experiment.

Results indicated that neutral treatment led to larger, multilayered MXene features, while the acidic treatment produced the most exfoliated and conformal coating, with a sheet thickness of about 8 nm. Alkaline treatment resulted in smaller flakes and visible pitting on the PET surface, highlighting that the chemical environment influenced coating size, stacking, oxidation, and substrate morphology.

Spectroscopic analysis revealed treatment-dependent changes in PET carboxylates and MXene surface states. The neutral sample retained the highest Ti–C fraction, whereas acidic and alkaline samples showed increased Ti–O and TiO2 contributions, with the alkaline sample having the lowest Ti–C fraction. These findings suggest variations in hydrogen bonding and potential localized Ti–O–C interactions, though no specific covalent bonds were confirmed.

X-ray diffraction showed that the treatment also affected PET structure, with apparent crystallinity decreasing from 65.30% in untreated PET to 56.20% after neutral treatment, 39.24% after acidic treatment, and 63.47% after alkaline treatment. The acidic condition caused the greatest disruption of ordered PET domains.

Under infrared irradiation, MXene-coated fabrics exhibited mean surface temperatures of 82 ± 1.2 °C for neutral, 76 ± 1.5 °C for acidic, and 81 ± 1.1 °C for alkaline treatments, with photothermal conversion efficiencies of 86%, 77%, and 84%, respectively. The uniform acidic coating did not achieve the highest temperature, indicating that coating architecture and morphology are crucial to performance.

Bacterial inhibition under infrared light reached 99.2% for E. coli with acidic-treated fabric and 98.8% for S. aureus with alkaline-treated fabric. Ice melting times were reduced to 21–22 minutes for coated fabrics, compared to 30 minutes for untreated PET. Maximum electromagnetic shielding in the X-band was 21.73 dB for the acidic sample. After 24 hours of UV exposure, methylene-blue removal was 98.4% for alkaline-treated, 97.3% for acidic-treated, and 96.6% for neutral-treated fabrics.

The treated fabrics maintained tensile strengths of 301–321 N, equating to 111.5–118.9% of the untreated PET value, with abrasion mass loss between 0% and 1% after 20,000 Martindale cycles. However, alkaline exposure led to localized PET degradation, and some measurements were based on single observations. Long-term performance under repeated laundering, UV exposure, perspiration, deformation, or environmental aging was not assessed.

In conclusion, the study highlights pH as an effective variable for tailoring the properties of Ti3C2Tx-coated PET textiles. The results underscore the combined effects of interfacial chemistry, MXene oxidation, termination chemistry, coating morphology, and PET modification on performance.