• • MS constitutes 80–90 wt.% of MXene synthesis by-products; its valorization directly reduces precursor waste and raw material costs, addressing the low yield (typically <20%) that hinders scalable MXene production.
• • The 80 wt.% MS/CNF film delivers 52.3 dB X-band EMI SE at 0.57 mm thickness, exceeding the 20 dB commercial threshold for industrial shielding by a factor of 2.6, enabling thinner, lighter shields for aerospace and portable electronics.
• • Tunable EMI SE >53.9 dB at 0.50 mm across X-, Ku-, K-, and Ka-bands (8.2–40 GHz) demonstrates broadband effectiveness, critical for 5G/6G communication and radar systems where single-band shields fail.
• • Photothermal heating to 100 °C in 80 s under 100 mW/cm² (equivalent to 1 sun) provides a dual-functionality platform for thermal therapy and wearable heaters, with potential for on-demand de-icing or clinical hyperthermia.