Ceramic membranes have been being increasingly employed in wastewater treatment,water purification and other industrial separation owing to their merits such as high-stability,anti-oxidation,long lifespan and environmental friendliness.Current ceramic membranes are mainly used in microfiltration and ultrafiltration processes,their precise separation application is still in infancy.Developing high-performance ceramic-based novel separation membranes is a key step to further expand their harsh and precise separation applications.Metal–organic frameworks(MOF)have great potential in separation membranes in terms of their designability and diversity.To address these issues,herein,considering the physi-chemical properties of typical pollutants(oil nano-emulsion and inorganic salt),we first design-fabricated high performance robust zirconia(Zr O2)ceramic membrane for highly efficient and operation-stable separation of not only simulated nano-emulsion but real industrial oily wastewater.Moreover,the models and mechanism of membrane fouling were proposed.Then,via a combined strategy consisting of substarte surface engineering and missing-linker design,we design-fabricated ceramic-based ultrathin MOF membranes with intra-crystalline missing-linker defects,enabling promising performance and long-term stability for the precision separation of hypersaline wastewater.Detailed structural characterization and molecular dynamics simulations were employed for qualitative and quantitative identification for intra-crystalline missing-linker defects.We furthermore proposed the positive atomistic-level mechanism of intra-crystalline-defect enhanced water permeation performance.The main results and conclusions are shown as follows:(1)To address the issue of challenging nano-emulsion separation,robust underwater superoleophobic Zr O2 membranes were specially design-fabricated,enabling its highly efficient and operation-stable separation.Then,the models and mechanism of membrane fouling were revealed.The best-performing Zr O2 membrane,fabricated at low sintering temperature,have relatively uniform sub-100 nm pores and underwater superoleophobic surface properties,enabling efficient separation of oil nano-emulsions and real oily wastewater.Such Zr O2 membranes possess not only outstanding separation performance under long-term operation but robust structural stability at harsh conditions.A combined model of intermediate pore blocking and cake filtration dominated membrane fouling behavior.Specifically,at high p H value(especially>p H(IEP)),membrane fouling was effectively mitigated due to a dominant role of electrostatic repulsion interaction at membrane–oil interface.Our Zr O2 membrane is the first reported in literature that can effectively reject nano-sized oil droplets(~18 nm)with over 99%oil rejection.Moreover,the Zr O2 membrane has also been challenged with real degreasing wastewater with very high oil content(~4284 mg L–1)and p H(~12.4)and delivered consistently high separation performance over many operation cycles.(2)To address the challenge of ultrathin membrane fabrication,we design-fabricated ceramic-based MOF membranes with intra-crystalline missing-linker defects(i.e.,ML-Ui O-66)via a combined strategy of surface engineering and molecule-level missing-linker design.We report a simple and cost-effective solution-based synthesis method for rational design of an ultrathin Ui O-66 MOF membrane(sub-100 nm thickness,90±10 nm)by introducingγ-Al2O3 interlayer with low-roughness and abundant nucleation sites onto Zr O2 substrate.These strategies overcome the challenging fabrication issue of well inter-grown Ui O-66 membrane via in situ solvothermal growth,and significantly reduced the membrane thickness.Besides implementing a facile thinning protocol,a molecular-level intra-crystalline defect chemistry strategy is proposed to rationally design a robust ultrathin ML-Ui O-66 membrane(104±13nm)for positively improving membrane permeation performance.(3)To address the challenge of hypersaline wastewater treatment,we achieved the excellent separation performance and long-term stability of ML-Ui O-66 membrane,and then proposed the mechanism of defect-enhanced permeation performance.Ultrathin ML-Ui O-66membranes are demonstrated to have not only excellent stability toward hot saline,chlorine,alkaline and acidic solutions,but also almost complete salt rejection and more importantly high water flux(~29.8 L m-2 h-1).Meanwhile,its excellent chlorine resistance is expected to address the insufficient operational stability of MOF membranes.Then,detailed structural characterizations are employed to analyse the intra-crystalline missing-linker defects.Moreover,molecular dynamics simulations shed light on the positive atomistic role of these defects,which are responsible for substantially enhancing structural hydrophilicity(water contact angle from 83±2°to 50±5°)and enlarging pore window(pore size from 0.568 nm to 0.628 nm),consequently allowing ultra-fast water transport via a lower-energy-barrier pathway across three-dimensional sub-nanochannels during pervaporation process.Unlike common unfavorable defect effects,the present positive intra-crystalline defect engineering concept at the molecular level is expected to pave a promising way toward not only rational design of next generation MOF membranes with enhanced permeation performance,but additional water treatment applications.In summary,the research topics in this thesis are hopefully expected to provide some scientific and technical reference for broadening the potential of ceramic-based membranes for challenging water treatment application,paving a promising way toward design of high-performance next-generation ceramic membranes for more water treatment applications. |