Application And Performance Enhancement Of Novel Polyelectrolyte Complexes And Carbon Materials In Membrane Separation For Liquid Mixtures

Membrane separation has the superiorities of high efficiency,less energy consumption,low environmental footprint and extensive applicability,considerable achievements in membrane fabrication and application have been made in recent years.In design of high-quality membranes,developing novel functional materials is of great significance to realize excellent separation performance.In this thesis,the utilization of polyelectrolyte complexes（PECs）,graphene oxide and carbon nanotube in membrane preparation and separation was investigated,and related issues that hindered their applications were solved.The prepared membranes were competent in solvents dehydration,brine desalination and organic solvent forward osmosis（OSFO）to enhance separation performances.Processable sphere-like nanoscale PECs and their homogeneous polyelectrolyte complex membranes（HPECMs）were synthesized.Spherical PECs possessed higher charge density than conventional needle-like ones.The HPECMs with sphere-like PECs displayed a smooth,homogeneous and dense surface,the hydrophilicity of which increased with ionic complexation degrees of PECs.When subjected to ethanol dehydration,the effects of ionic complexation degree,feed temperature and water concentration on pervaporation performances were systematically investigated.For HPECM 0.57,the permeation flux was 2.93 kg m^-2 h^-1,and the water content in permeate reached up to 99.38 wt%for 10 wt%water in feed at 70°C.Compared with the HPECMs with needle-like PECs,the flux through HPECMs with sphere-like PECs was nearly doubled with better dehydration performance.Sulfonated graphene oxide was prepared via grafting sulfonate groups on graphene oxide sheets,which possessed enhanced transport capacity compared with graphene oxide.After coated with an ultrathin hydrophilic polyelectrolyte layer（a mixture of carboxymethylcellulose sodium and poly（4–styrenesulfonic acid-co-maleic acid）sodium）,sulfonated graphene oxide composite membrane was obtained.The synergistic effect of highly enhanced water adsorption from the polyelectrolyte layer and ultrafast permeation channels from sulfonated graphene oxide facilitated the rapid and selective transport of water molecules through the membrane,ensuring excellent isopropanol dehydration performances.In addition,the effect of polyelectrolyte layer composition and feed temperature on pervaporation performances were researched.At70°C,the flux could reach up to 3.67 kg m^-2 h^-1 with 99.90 wt%water content in permeate.The mechanical strength and interfacial adhesion of prepared membrane were strong enough,which contributed to maintain stable performance in practical pervaporation operations.A novel method was presented to fully utilize the atomically smooth outer wall of carbon nanotube to transport water molecules.Carbon nanotubes were purified and longitudinal partially unzipped,which had a unique core-shell heterostructure with nanotube as core and graphene oxide nanoribbons as shell.The special core-shell structure was conducive to realize vertically molecular transport,shorter interlayer diffusion and accelerate permeation velocity.Composite membrane was developed by coating hydrophilic polyelectrolyte on stacked unzipped nanotubes,which displayed excellent pervaporation performances in ethanol,isopropanol and acetone dehydration.Moreover,the composite membrane could effectively reject Na Cl,Ca Cl₂ and Mg Cl₂（99.99%）through electrostatic repulsion and obtained high water flux in pervaporation desalination.This facile method could provide new inspirations for developing novel high-efficiency carbon nanotube composite membranes applied in water treatment.The great potential of graphene oxide membrane utilized in OSFO process was demonstrated for the first time.Graphene oxide membrane had superior chemical inertness and highly laminated interlayer structure,when subjected to OSFO process in methanol system,graphene oxide membrane with large-sized sheets displayed more satisfactory performances than that with smaller sheets.With the membrane thickness decline or the draw solution concentration increase,both the methanol flux and reverse solute flux elevated.Graphene oxide membrane was also competent in OSFO process to recover ethanol,isopropanol,etc.In the enrichment of target product via OSFO,Rhodamine B,Lumogen Red 300 and atorvastatin calcium were selected as model feed solute,graphene oxide membrane exhibited ideal rejection and higher solvent flux than polyamide membrane,evidencing the capacity in product enrichment and simultaneous solvent recovery in OSFO process.