Effect of alkoxysilane chain length on the surface, stability, sorption and oil–water separation properties of novel superhydrophobic porous sorbent materials produced using innovative drainage technique in scCO2 atmosphere

[Display omitted] •Alkoxysilane-modified sorbent materials with different side chain lengths were produced.•Sponge coating was achieved through the expansion of sponge space induced by scCO2.•For MS-METES, MS-OTES and MS-HDTMS, WCA was determined as 153.0°, 159.4° and 165.4°, respectively.•Sorption capacity decreased from 122.2 g/g to 90.4 g/g with increasing chain length of alkoxysilane.•The superhydrophobic sorbent exhibited remarkable flexibility and excellent reusability. Alkoxysilanes play an important role in the development of new superhydrophobic sorbent materials with high sorption capacity for the cleanup of oil spills from water. Here, three different alkoxysilanes with 1, 8 and 16 carbon (C) chains were used for the first time to elucidate the role of alkoxysilanes and to determine the relation between the functional alkyl chain length of alkoxysilane compound within the coating formulation and the surface, sorption and separation properties of novel superhydrophobic sorbent materials fabricated in scCO2 atmosphere. Both the modification of activated halloysite nanotube (HNT) with each methyltrietoxysilane (METES), octyltriethoxysilane (OTES) and hexadecyltrimethoxysilane (HDTMS) separately and the direct fabrication of melamine sponge (MS)-HNT/alkoxysilane hybrid composite sorbents (MS-METES, MS-OTES and MS-HDTMS) were achieved by innovative drainage technique in scCO2 atmosphere. The surface properties of superhydrophobic sorbents were examined using contact angle, SEM, EDS, FTIR, XPS and 29Si-MAS NMR techniques. Maximum sorption capacity of melamine sponge-based hybrid materials decreased from 122.2 g/g to 90.4 g/g as the chain length of alkoxysilane was increased from C1 to C16. Water contact angle, density and porosity of superhydrophobic MS-METES, MS-OTES and MS-HDTMS sorbents were determined to be 153.0°, 13.56 mg/cm3 and 99.10 %; 159.4°, 16.58 mg/cm3 and 98.90 %; and 165.4°, 18.90 mg/cm3 and 98.75 %, respectively. All sorbents exhibited excellent thermal stability, good chemical stability, good robustness, and high mechanical durability. Experimental results revealed that the novel coating technique applied to porous MS have a significant potential for the direct fabrication of new superhydrophobic and superoleophilic sponge-based sorbent materials.