| Water resources scarcity and water pollution have been increasingly being aggravated in recent years.High salinity wastewater,generated by seawater desalination and industry wastewater,possesses complicated composition and physicochemical property,thus it is difficult to treat high salinity wastewater.Among various technologies,membrane distillation is an emerging desalination technology based on the vapor pressure difference across a porous hydrophobic membrane.Typically,membrane distillation is carried out at relatively low operating temperature and insensitive to salt concentration.Thus,it can utilize low-grade or waste heat to generate high-quality drinking water from seawater or high salinity water with high recovery.Therefore,membrane distillation for high salinity water treatment provides an attractive economic and green solution to develop a zero-discharge water desalination process.Unfortunately,the current inorganic membrane materials possess a number of deficiencies when considering them for long-term operation in membrane distillation such as poor hydrophobicity and thermal stability,membrane fouling and regeneration problems.Therefore,structure-designed membranes that can fulfill the special requirements of membrane distillation process are urgently pursued for practical application of high salinity wastewater treatment.Herein,we proposed a design strategy for fabrication of a novel ceramic-CNTs composite membrane with excellent membrane distillation performance.The ceramic-CNTs composite membranes possess highly thermal stable superhydrophobicity due to the excellent thermal stability and superhydrophobicity of CNTs,which can continuously inhibit water penetration and membrane wetting.Importantly,the ceramic-CNTs composite membranes also possess good electro-conductivity due to the encouraging electrochemical property of CNTs.Thus it provides a strategy for achieving excellent anti-organic-fouling resistance under electrochemical assistance,which is beneficial for highly efficient membrane distillation water treatment for high salinity wastewater.The main research topics,results and conclusions are shown as follows:(1)With a low cost bauxite mineral and NiO as starting materials,nickel aluminate spinel hollow fiber membranes were prepared by immersion-induced phase inversion and sintering technique,which exhibited a typical self-supported and asymmetric macro-porous structure.Effects of sintering temperature on membrane properties,such as phase variation and quantification,morphology,pore structure and mechanical strength,were investigated systemically.When sintering temperature was 1300 °C,the NiAl2O4 phase was completely formed,and mechanical strength was up to 63.6 MPa.Compared to traditional Al2O3 hollow fiber membranes sintered at 1500 °C(48.6 MPa),the as-prepared nickel aluminate spinel hollow fiber membranes not only presented lower fabrication costs including raw materials and sintering,but also exhibited higher mechanical strength.(2)The versatile and effective chemical vapor deposition was employed to in situ grow CNTs both on hollow fiber membrane substrate surface and inside pore channel walls of large-sized finger-like voids,thus forming ceramic-CNTs composite membrane.The specific influence of preparation parameters such as catalyst loading,reaction temperature and time,on composite membranes morphology and performances was studied and presented.It is noteworthy that different kinds of CNTs distribution states were observed though different preparation paramters.Typically,considering different reaction time,two different kinds of membrane structures in the ceramic-CNTs composite membranes were obtained,including partially covered CNTs network and fully covered CNTs network.(3)These two kinds of composite membranes with different CNTs distribution states were compared in hydrophobic property,gas and water permeability and MD performance.The optimized composite membranes with fully covered CNTs network had about 170° water contact angle,and maintained extremely highly thermal stable water contact angle after boiling in water for 24 h.Comparing with ceramic-FAS membranes and ceramic-SiNCO membranes under a similar accelerated test,the ceramic-CNTs composite membranes outperformed other hydrophobic ceramic-based membranes in highly thermal stable superhydrophobicity.In addition,due to the abundant interconnected pores and high porosity of CNTs network structure,the composite membranes exhibited a stable permeation flux and salt rejection above 99 % for high salinity water desalination.Interestingly,under electrochemical assistant,the membranes not only exhibited an excellent anti-fouling resistance,but also presented a competitive permeation flux of 24.1 L·m-2·h-1 and a stable high salt rejection of 99.4% in the treatment of high salinity wastewater. |
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