Construction Of Top Layer On α-Al₂O₃ Ceramic Membrane And MTBE/H₂O Separation Performance

The petrochemical,biomedical and mechanical processing usually generates wastewater containing volatile organic compounds（VOCs）,which are harmful to human health and destructive to the environment.Therefore,VOCs should be removed before the release of wastewater.Membrane separation based on pervaporation has received more attention in removing VOCs from wastewater due to the unique advantages such as high separation efficiency,low energy consumption,small footprint,and continuous operation.The present thesis constructs either ZnO nanorod arrays（ZNA）or methyl-modified silica layer（MSL）on the porousα-Al₂O₃ ceramic membranes.It investigates the separation of methyl tert-butyl ether（MTBE）,a kind of VOCs,from aqueous solution by the obtained membranes.Porousα-Al₂O₃ ceramic membranes were prepared by dry-pressing and solid-phase sintering method usingα-Al₂O₃ powder as the primary raw material and polymethyl methacrylate（PMMA）as the pore-forming agent.It is found thatα-Al₂O₃ceramic membranes with the most probable pore size ranging from 40 to 450nm can be obtained by adjusting the parameters such as the shape and particle size of Al₂O₃powder,the particle size and concentration of PMMA,and the ball-milling time.ZnO seed layers were grown on porousα-Al₂O₃ ceramic membranes（ZSL@Al₂O₃membrane）by dipping theα-Al₂O₃ ceramic membranes into the concentrated ZnO sol with ethanol as a solvent for 5 min and then annealing at 420℃for 1 h.The construction of ZnO nanorod arrays on the Al₂O₃ membranes（SZNA@Al₂O₃membrane）was realized by hydrothermally treating the ZSL@Al₂O₃ membranes in the aqueous solution of zinc nitrate hydrate（0.05mol/L）and hexamethylenetetramine（0.05mol/L）at 90℃for 8 h.Hydrophobic SZNA@Al₂O₃ membranes（F-SZNA@Al₂O₃ membranes）were obtained by the post-grafting approach using1H,1H,2H,2H-perfluorooctyltriethoxysilane（PFOTES）as a modifier.The F-SZNA@Al₂O₃-260 membranes,in which theα-Al₂O₃ ceramic membranes have the most probable pore size of 260 nm,are superhydrophobic,with a water contact angle of 157°.The membranes exhibit a total flux of 0.611 kg m^-2 h^-1,an MTBE/H₂O separation of 57.4,and an MTBE concentration of 73%in the permeate flux under the operating conditions as follows:a feed temperature of 25℃,an MTBE concentration of 4.6 wt%,and a feed flow rate of 300 m L min^-1.The separation is realized by pervaporation which complies with the solution-diffusion mechanism.Methyl-modified silica layer（MSL）was deposited on porousα-Al₂O₃ ceramic membranes with methyltrimethoxysilane（MTMS）as a precursor and pre-synthesized mesoporous silica microspheres as dopants by the sol-gel reaction and dip-coating method.The NMR spectra revealed that MTMS evolves gradually from an oligomer to a highly cross-linked methyl-modified silica species.Methyl-modified silica species and pre-synthesized mesoporous silica microspheres combine into hydrophobic mesoporous MSL.MSL makes theα-Al₂O₃ ceramic membranes transfer from amphiphilic to hydrophobic and oleophilic.The MSL-supportedα-Al₂O₃ ceramic membranes（MSL-10）exhibit an MTBE/water separation factor of 27.1 and a total flux of 0.448 kg m^-2h^-1,and an MTBE concentration of 56%in the permeate under the following operating conditions:a feed temperature of 30℃,an MTBE concentration of4.6 wt%,and a feed flow rate of 200 m L min^-1.The mesopores within the MSL provide a pathway for the transport of MTBE molecules across the membranes.The presence of methyl groups on the external and inner surface is responsible for the favorable separation performance and the outstanding long-term stability of the MSL-supported porousα-Al₂O₃ ceramic membranes.