Preparation Of Multi-walled Carbon Nanotube-loaded Superhydrophobic Sponge And Its Application In Oil-water Separation

In recent years,with the progress of social economy and the continuous development of oil industry and marine transportation industry,the problem of industrial oily wastewater discharge has become more and more prominent and marine oil spill accidents occur frequently,which has caused serious environmental pollution problems due to the lack of effective treatment process and brought great challenges to environmental management.Superhydrophobic/superoleophilic sponge materials are widely used in the treatment of oily wastewater due to their good elasticity,high separation efficiency and excellent selective absorption/separation ability.Polyurethane(PU)sponge is a three-dimensional porous material with excellent characteristics such as low density,low price,good elasticity and high absorption capacity.Meanwhile,its surface contains a large number of amino and hydroxyl groups,which are easy to be chemically modified and are ideal substrates for the preparation of superhydrophobic/superoleophilic materials.Hydroxylated multi-walled carbon nanotubes(MWCNTs-OH)are two-dimensional carbon nanomaterials that can be used as adsorbent materials due to their high aspect ratio,low density and good environmental chemical stability,while the hydroxyl groups on their surfaces are easy to be chemically modified and can be enhanced by surface grafting specific organic groups to enhance their surface hydrophobic/oleophilic properties.In this study,three hydrophobic long-chain siloxanes were selected as the substrate for modification of carbon nanotubes and sponges,and the effects of different coupling agents and coupling reaction times were optimized,and superhydrophobic sponges were obtained by a onestep method.The superhydrophobic sponges were characterized by scanning electron microscopy(SEM),Fourier transform infrared spectroscopy(FT-IR),interfacial rheometry,potential analyzer and thermogravimetric analyzer(TG),and the changes of surface morphology,chemical composition and wettability of polyurethane sponges before and after modification were investigated,and the effects of different temperatures and ionic strength on the oil absorption ability of superhydrophobic sponges were measured.The main research results of this thesis are as follows.(1)Dimethyl octadecyl[3-(trimethoxy silicon)propyl]ammonium chloride(OTA),hexadecyltrimethoxylsilane(HDTMS)and octadecyltrichlorosilane(OTS)were selected as coupling agents to react with hydroxylated carbon nanotubes and polyurethane sponge(PU),respectively,and carbon nanotubes were loaded onto the sponge to construct micro and nano rough structures while reducing the surface energy of the sponge.The effect of coupling reaction time on the hydrophobicity of the sponge was also investigated,and the optimal modification conditions were finally determined as follows:OTS was used as the coupling agent,and the coupling agent was fully reacted with hydroxylated multi-walled carbon nanotubes and PU sponge on the surface of the multi-walled carbon nanotubes and PU sponge under magnetic stirring conditions for 24 h.The coupling agent was grafted onto the surface of the multi-walled carbon nanotubes and PU sponge.Then,the carbon nanotubes were loaded onto the polyurethane sponge by ultrasonic dip coating.The water contact angle(WCA)of the prepared superhydrophobic sponge(OTS-CNTs/PU)was 151.3±1.2°.(2)The sponges were characterized before and after modification.Scanning electron microscopy photographs showed that the original three-dimensional porous structure of the sponge was not destroyed after modification,and the loading of multiwalled carbon nanotubes led to the formation of a micro-and nano-rough structure on the sponge surface;the changes in the chemical composition of the sponge surface before and after modification were analyzed by FT-IR,which proved that the coupling agent had been successfully grafted onto the sponge surface.The water contact angle of the modified sponge was tested by interfacial rheometer,and the results showed that the modified sponge has superhydrophobicity.(3)The mechanical properties and thermal stability of the superhydrophobic sponge were tested.The results show that the superhydrophobic sponge can withstand higher strength pressure,and the thermal stability is significantly improved after the modification,and the surface wettability of the sponge is not affected by a certain degree of heat,and the water contact angle is still more than 150°(151.0±0.9°)even after 300 minutes at 80℃.(4)The oil absorption capacity test showed that OTS-CNTs/PU has a high adsorption capacity and can absorb 14.99 to 86.53 times its own weight of oil,depending mainly on the density and viscosity of the oil.After repeated use for 10 times,its absorption capacity remained at more than 90%of the initial absorption capacity,with good recycling performance.(5)The changes of oil absorption capacity of the sponge were measured at different temperatures and ionic strengths.The viscosity of the oil decreased with increasing temperature and the hydrophobicity of the sponge weakened with increasing ionic strength,which affected the oil absorption capacity of the sponge,and thus the absorption of oil by the superhydrophobic sponge was based on the combined effect of capillary and hydrophobic forces.