Superhydrophobic coatings have been widely developed to endue the materials with multi-functionality, including antibacterial[1], self-cleaning[2], antiseptic[3], and oil-water separation capacities[4]. Inspired by the natural interface structure of lotus leaves, the fabrication of micro/nano rough structures and reduction of surface free energy are the two main design approaches of superhydrophobic coatings[5]. Many studies have constructed the micro/nano rough structures from different raw materials (metals[6], alloys[7], ceramics[8]) by various fabrication methods[9], e.g. electrochemical etching[10], sol-gel processing[11], template syntheses[12], chemical vapor deposition[13], electrochemical method[14], layer-by-layer deposition[15]. However, most of these strategies are tedious, expensive, and resource intensive. On the other hand, the low surface energy contributes to the wetting transformation from hydrophilicity to superhydrophobicity[16]. Although, trifluoromethyl groups exhibit the lowest possible surface energy, the released toxic substance from fluorinated polymers are a significant source of water pollution and even a threat to human health. Therefore, it’s very necessary to develop a facile and green approach to fabricate superhydrophobic coatings[17]-[18].
Lignocellulose is an economic and sustainable material, which is widely abundant in nature. Lignocellulose-based materials and their derivatives are sustainable, degradable, and environmentally friendly [19, 20]. Nanofibrillated lignocellulose (NFC) can be separated from lignocellulose using enzymatic pretreatment, oxidation pretreatment, or alkaline pretreatment followed by mechanical treatment. Owing to its nanoscale structure, modifiableness, biodegradability, and environmental friendliness[21–23], NFC has been extensively used in many fields such as antibacterial[24], anti-corrosion[25], UV protection[26], packaging[27], and gas barrier[28]. The surface of NFC contains a large number of hydroxyl groups, which are easily modified by substances with low surface energy[29]. NFC has become one of the most promising green raw materials for the preparation of the fabrication of superhydrophobic coatings.
Surface grafting by a small amount of organic matter with low surface energy is an efficient and convenient way to form a superhydrophobic surface. Moreover, the surface roughness of NFC can be improved by organosilicon compounds, which have many good characteristics, including environmental protection, non-toxic, antioxidation, high-temperature and corrosion resistance. Herein, fluorine-free and environmentally benign NFC-based multifunctional superhydrophobic coatings (NMSC) were designed and fabricated by a facile coupling reaction of environmentally friendly ethyl orthosilicate and cetyl trimethoxysilane (Fig. 1a, b). Ethyl orthosilicate can be hydrolyzed into organosilicon by the breaking reaction of oxo-silicon bond catalyzed by ammonia water (Fig. 1c), which will provide a surface roughness for NFC. The hydrolyzation of hexadecyltrimethoxysilane into long-chain alkyl groups decreased the surface energy of NFC. The physicochemical, water-resisting, anticorrosive, and antibacterial properties of NMSC were systematically investigated.