Preparation And Properties Of Oil/water Separation Materials In Harsh Environment

With the development of economy,the discharge of oily wastewater with complex components is increasing and the marine oil spill accidents occur frequently,which bring new challenges to oil/water separation.Compared with the traditional methods,controlling the wettability of solid-surface to realize oil/water separation has attracted more and more attention.Especially,hydrophilic and underwater oleophobic materials are easier to prepare and more feasible in large-scale oil/water separation.Therefore,the Co₃O₄ with stable chemical properties was introduced to modify the wettability of stainless-steel mesh and enhance its oil/xwater separation performance in harsh environment.Then,TiO₂ was introduced to improve the material's self-clearning performance by taking advantages of the strong oxidizing fr-ee radicals produced by photocatalysis.At the same time,in the aid of a series of characterization,the surface properties of as-prepared materials w ere correlated to their oil/water separation and self-cleaning performance.Through simple hydrothermal and calcination process,Co₃O₄ can be successfully loaded onto the stainless-steel mesh.XRD,SEM and CA were used to characterize and analyze the surface properties of the Co₃O₄ mesh.After loading Co₃O₄,the wettability of the stainless-steel mesh shifted from hydrophobic and underwater oleophobic to superhydrophilic and underwater superoleophobic.In the meantime,the effects of preparation conditions such as cobalt source,reactant ratio and hydrothermal reaction time on its morphology and wettability were also investigated.The optimum preparation conditions are as follows:cobalt nitrate is used as the cobalt source,reacting with urea at the ratio of 1:5 and the hydrothermal reaction time was 6 h.Two layers of Co₃O₄ can be found on the surface of th e stainless-steel mesh,the inner layer is n eedle-like Co₃O₄,and the outer layer is Co₃O₄ sheets.This unique morphology enhanced its underwater oleophobicity.In addition,the prepared Co₃O₄ mesh can effectively separate various types of oil/water mixtures with high efficiency?>99.4%?and high flux?>75000 L·m-2·h-1?.The oil/water separation in harsh environment was simulated by employing corrosive liquid and sandpaper abrasion.The prepared Co₃O₄ mesh is insusceptible to pH,and can maintain its underwater superoleophobic character in a wide pH range.What's more,high concentration of acidic,alkaline and salt solution will not affect the oil/water separation efficiency,showing good chemical stability.In addition,after 40 sandpaper abrasion cycles,its underwater oil contact angle can still maintain above 148°,exhibiting high mechanical stability.Furthermore,TiO₂ was introduced via self-assembly method,with tetrabutyl titanate acted as titanium source.The surface properties of the prepared Co₃O₄/TiO₂ mesh were characterized and analyzed by XRD,SEM,EDS and CA.In addition,the preparation conditions were optimized by changing the depositional position of TiO₂ and the number of self-assembly times to improve its underwater oil-repellent property.The optimum preparartion conditions are as follows:TiO₂ deposited on the top of the Co₃O₄ mesh with 5 times of self-assembly.The prepared Co₃O₄/TiO₂ mesh not only retains the morphology of the original Co₃O₄ mesh,but also improves its underwater oil repellency due to the loading of hydrophilic TiO₂.After being contaminated by oleic acid,the wettability of Co₃O₄/TiO₂ mesh can be recovered by ultraviolet irradiation for 40 min in the aqueous environment.Cormpared with the original Co₃O₄ mesh,the Co₃O₄/TiO₂ mesh displayed better self-cleaning performance,oxwing to the strong oxidizing free groups produced by the reaction of TiO₂ with water under ultraviolet irradiation.After three self-cleaning cycles,the underwater oil contact angle of the prepared Co₃O₄/TiO₂ mesh can stili reach 148°,indicating good recyclability.