Construction Of Graphene-based Porous Composite Structures And Their Oil-water Separation Performance

At present,the frequent oil-leakage accidents and the increasingly serious pollution caused by oily wastewater pose a certain threat to human health and the ecological environment,so the treatment of oily wastewater is extremely urgent.Graphene,a single-layer two-dimensional crystal closely arranged into a honeycomb structure in the form of sp²hybrid,which has a very large specific surface area,excellent mechanical properties,natural lipophilic hydrophobicity and thermal stability.Compared with graphene,graphene oxide（GO）is easy to be modified,and has low production cost,and the potential for mass production.In addition,GO has oxygen-containing functional groups such as hydroxyl,carboxyl,carbonyl,and epoxy groups,which make it hydrophilic.Reduced graphene oxide（r GO）,as the reduced product of graphene oxide,has physical and chemical properties similar to those of graphene,especially retaining the oleophilic and hydrophobic properties of graphene.Possessing superwetting and porous structure,the graphene-based porous composite structure can be used as an oil/water separation material.At present,the practical application of oil/water separation materials is often affected by high investment,complex process and toxic chemicals.Therefore,it is necessary to find a low-cost,green and simple method for oil-water separation.To this end,this thesis explores the preparation of graphene-based porous materials and their oil/water separation properties.The specific work is as follows:A novel graphene oxide-connected cotton fibers（GOCCF）membrane was fabricated by simply soaking cotton in graphene oxide（GO）aqueous-alcoholic suspension followed by air-drying;super-hydrophilic/underwater super-oleophobic graphene oxide coated melamine sponge（GO@MS）and super-hydrophobic/super-oleophilic reduced graphene oxide coated melamine sponge（r GO@MS）were prepared via dip-coating of GO sheets onto melamine sponge（MS）and subsequent chemical reduction,respectively.The morphology,structure and wettability of these materials as well as the separation properties,chemical stability and recyclability of various oil/water mixtures were studied.The following conclusions are reached:The synergistic effect of the rough surface and the hydrophilic polar groups on the GO nanosheets endows the GOCCF membrane with superhydrophilicity and underwater superoleophobicity.The GOCCF membrane can be applied to oil/water separation,and exhibits high separation efficiency for separating water from various oils driven by gravity.The GOCCF membrane also shows remarkable antifouling behavior and recyclability with maintaining a high separation efficiency over 99.8%and an ultra-high flux about 95,000 L m^-2 h^-1 in the whole separation processes repeated for 30 cycles.These results suggest that the GOCCF membrane could be a potential material for practical oil/water separation.To achieve oil/water separation using both absorption and filtration regardless of the oil/water density relationship,GO@MS and r GO@MS were prepared.The results showed that GO@MS and r GO@MS have the following characteristics:first,both GO@MS and r GO@MS can preserve their original wettability in harsh environments containing acidic,alkaline,saline,and hot waters;second,the GO@MS and r GO@MS show excellent capability for selective absorption of water and oil respectively,with high capacities of 72.3-136.5 g g^-1 and excellent recyclability;third,The compressed GO@MS and r GO@MS also exhibit high separation efficiency of about 99%and ultra-high permeation flux above 1.62×10⁵ L m^-2 h^-1 for separating different oil/water mixtures containing light and heavy oils through filtration driven by gravity,respectively.Furthermore,a bidirectional separation setup assembled with the compressed GO@MS and r GO@MS was constructed,which demonstrates high efficiency for continuously separating different oil/water mixtures of any oil density.