As shown in the DTG results, MD reaches the point of maximum thermal decomposition rate at 362.3°C, which indicates the dehydration of surface hydroxyl groups, which is consistent with the OSMD[40]. OSMD shows another jump discontinuity at 561.8°C, which may be due to the loss of grafted octadecyl and sulfonyl groups[41]. Throughout the process, the overall mass loss of MD was 7.6%, while the overall mass loss of OSMD was 8.6%, this indicated that diatomite was successfully modified, while the support itself has excellent thermal stability.

The contact angle serves as a quantitative indicator of surface wettability, which quantifies the angle formed between the interface of the liquid or vapor and the solid surface. According to the Young-According to the Young-Laplace equation, the morphology of a droplet is influenced by the relative hydrophobic or hydrophilic properties of the material’s surface with respect to the liquid. A larger contact angle corresponds to a greater repulsive force exerted by the droplet on the surface, signifying a relatively higher degree of hydrophobicity of the material’s surface[24]. As depicted inFigure 3D (a) , diatomaceous earth exhibits pronounced hydrophilicity owing to the abundance of surface Si-OH groups[41]. Conversely, the contact angle of OSMD increased to 133.5° following additional octadecyl modification, indicative of its heightened hydrophobicity, which can also support that the successful modification of octadecyl.

Figure 4 . TG of MD and OSMD (A), DTG of MD (B) and OSMD (C), the contact angle of MD and OSMD (D)