In this study, sepiolite clay fibers were activated through hydrochloric acid acidification at various concentrations. The effects of different acid environments on the phase structure, morphology, and physicochemical properties of the activated sepiolite fibers were studied extensively. It was found that calcite impurities can be effectively removed when the acid concentration exceeds 1 M. Furthermore, the specific surface area of K-supported sepiolite fibers increases continuously with rising acid concentration, reaching 107.9 m²/g when the hydrochloric acid concentration is 7 M. The soot temperature-programmed oxidation (TPO) results demonstrated that K-supported sepiolite fibers acidified with 3 M HCl exhibited the highest catalytic activity, with T₁₀ and T₅₀ values of 323 °C and 348 °C, respectively. The 10 wt% K-supported sepiolite paper catalyst, using 3 M HCl-activated sepiolite fibers as the matrix, exhibited the lowest T₅₀ value of 436 °C and showed excellent stability compared to all other paper catalyst samples. This study on the activation of sepiolite-based catalysts under various acidic conditions advances the development of highly active and stable mineral catalytic materials and facilitates their practical application.

To develop energy-efficient building coatings with enhanced thermal energy storage performance, paraffin/sepiolite composite phase change coatings were prepared using ultrasonic-assisted acid-activated sepiolite as a supporting matrix. The effects of acid treatment duration on the structural properties of sepiolite and the performance of the resulting coatings were systematically investigated. The results showed that acid activation for 1 h produced the optimal pore structure, yielding a maximum internal specific surface area of 125.881 m² g⁻¹. Longer treatment durations (>2 h) caused structural degradation and possible deterioration of pore structure. The paraffin/sepiolite composite phase change material prepared with JK-1 h exhibited a latent heat of 77.29 J g⁻¹, outperforming that prepared with JK-2 h. Increasing the paraffin and CPCM contents enhanced the thermal storage capacity of the coatings; however, excessive CPCM loading deteriorated film integrity, resulting in cracking, reduced adhesion, and decreased hydrophobicity. Among all formulations, sample S3 demonstrated the best overall performance, with a latent heat of 33.51 J g⁻¹, a pull-off strength of 5.9 MPa, and a water contact angle of 102.53°. Thermal cycling tests further confirmed its excellent thermal reliability and reusability. These findings indicate that paraffin/sepiolite composite phase change coatings have considerable potential for reducing building energy consumption and improving indoor thermal regulation.