Preparation and mechanism of hydrophobic modified diatomite coatings for oil-water separation

Fig. Schematic diagram of diatomite modification process mechanism. The modification process is presented as follows: (1) The alkoxy group (–OCH2CH3) connected to Si in TEOS is hydrolyzed under alkaline conditions to produce silanol; The silica sol is formed by water condensation and self-condensation reaction. The surface of silica sol is linked with many hydroxyl groups. (2) The alkoxy group (–OCH3) linked to Si in HDTMS reacts with hydroxyl groups on the surface of silica sol and diatomite, and the long alkyl chain of HDTMS modifies the silica sol and diatomite to make them hydrophobic. (3) Simultaneously, the remaining HDTMS are dehydrated to form silanol and polycondensed to form poly-HDTMS. The silica nanoparticles are connected and covered on the surface of the powder particles through poly-HDTMS to make the surface of the inorganic powder organic. This is the core of this study. This figure was chosen as the cover because it represents the mechanism of this study. • Diatomite was successfully modified by HDTMS and TEOS to obtain hydrophobicity. • The mechanism and microstructure of diatomite modification were studied. • The Diatomite@POS Coating could be widely used in oil-water separation and self-cleaning fields. It remains a significant challenge to separate oil and water in the metallurgical industry. Therefore, there is an urgent need for a low-cost process to prepare hydrophobic and lipophilic materials in order to improve oil-water separation performance. The hydroxyl group on the surface of diatomite was modified by a polysiloxane reaction. The microstructure, chemical composition, and hydrophobicity before and after modification were studied by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Diatomite@POS/EP coating was prepared using the spraying suspension method, to endow various materials with excellent hydrophobic properties (ceramic, sponge, stainless steel, paper, and gauze). The SEM results show that many spherical particles were stacked on the modified diatomite disk, and new elements and structures were observed. The Diatomite@POS floated on the water indicates that the modification was successful. The contact angle between coating on porous diatomite ceramics and water could reach 147.5° when the mass ratio of Diatomite@POS: EP was 7:5. After 0–1000 cm wear test, and soaked in acid and alkali solution for 4 h, the coating could keep hydrophobicity, indicating that it features excellent wear resistance, acid, and alkali resistance. Ceramic sprayed with Diatomite@POS/EP and melamine sponges soaked in Diatomite@POS/EP were capable of effectively separating vacuum pump oil from water, which showed the promising self-cleaning performance of the ceramic surface. Besides, modified diatomite powder had great potential for application in waterproofing, self-cleaning, oil-water separation, and other fields.