Spray coating of polysulfone/poly(ethylene glycol) block polymer on macroporous substrates followed by selective swelling for composite ultrafiltration membranes

Polysulfone(PSF) is extensively used for the production of ultrafiltration(UF) membranes thanks to its high strength,chemical stability,and good processibility.However,PSF is intrinsically hydrophobic,and hydrophilic modification is always required to PSF-based membranes if they are intended to be used in aqueous systems.Facile strategies to prepare hydrophilic PSF membranes are thus highly demanded.Herein we spray coat a PSF-based amphiphilic block polymer onto macroporous substrates followed by selective swelling to prepare flat-sheet PSF UF membranes.The polymer is a triblock polymer containing PSF as the majority middle block tethered with shorter block of polyethylene glycol(PEG) on both ends,that is,PEG-b-PSF-b-PEG.We use the technique of spray coa ting to homogeneously dispense diluted triblock polymer solutions on the top of macroporous supports,instantly resulting in uniform,defect-free polymer coating layers with the thickness down to ~1.2 μm.The bi-layered composite structures are then immerged in ethanol/acetone mixture to generate mesoscale pores in the coating layers following the mechanism of selective swelling-induced pore generation,thus producing composite membranes with the mesoporous triblock polymer coating as the selective layers.This facile strategy is free from additional hydrophilic modification and much smaller dosages of polymers are used compared to conventional casting methods.The pore sizes,porositie s,hydrophilicity,and consequently the separation properties of the membranes can be flexibly tuned by changing the swelling duration and the composition of the swelling bath.This strategy combining spray coating and selective swelling is upscalable for the production of highperformance PSF UF membranes.

Uncovering the effect of poly(ethylene-co-vinyl alcohol)molecular weight and vinyl alcohol content on morphology,antifouling,and permeation properties of polysulfone ultrafiltration membrane:thermodynamic and formation hydrodynamic behavior

Various hydrophilic poly(ethylene-co-vinyl alcohol)(EVOH)were used herein to precisely control the structure and hydrodynamic properties of polysulfone(PSF)membranes.Particularly,to prepare pristine PSF and PSF/EVOH blends with increasing vinyl alcohol(VOH:73%,68%,56%),the non-solvent-induced phase separation(NIPS)technique was used.Polyethylene glycol was used as a compatibilizer and as a porogen in N,Ndimethylacetamide.Rheological and ultrasonic separation kinetic measurements were also carried out to develop an ultrafiltration membrane mechanism.The extracted membrane properties and filtration capabilities were systematically compared to the proposed mechanism.Accordingly,the addition of EVOH led to an increase in the rheology of the dopes.The resulting membranes exhibited a microporous structure,while the finger-like structures became more evident with increasing VOH content.The PSF/EVOH behavior was changed from immediate to delayed segregation due to a change in the hydrodynamic kinetics.Interestingly,the PSF/EVOH32 membranes showed high hydrophilicity and achieved a pure water permeability of 264 L·m^(–2)·h^(–1)·bar^(–1),which was higher than that of pure PSF membranes(171 L·m^(–2)·h^(–1)·bar^(–1)).In addition,PSF/EVOH32 rejected bovine serum albumin at a high rate(>90%)and achieved a significant restoration of permeability.Finally,from the thermodynamic and hydrodynamic results,valuable insights into the selection of hydrophilic copolymers were provided to tailor the membrane structure while improving both the permeability and antifouling performance.

Sea salt bittern-driven forward osmosis for nutrient recovery from black water: A dual waste-to-resource innovation via the osmotic membrane process

A dual“waste-to-resource”innovation in nutrient enrichment and recovery from domestic black water using a sea salt bittern(SSB)-driven forward osmosis(FO)process is proposed and demonstrated.The performance of SSB as a“waste-to-resource”draw solution for FO was first evaluated.A synthetic SSB-driven FO provided a water flux of25.67±3.36 L/m2 h,which was 1.5-1.7 times compared with synthetic seawater,1 M NaCl,and 1M MgCL.Slightly compromised performance regarding reverse solute selectivity was observed.In compensation,the enhanced reverse diffusion of Mg+suggested superior potential in terms of recovering nutrients in the form of struvite precipitation.The nutrient enrichment was performed using both the pre-filtered influent and effluent of a domestic septic tank.Over 80%of phosphate-P recovery was achieved from both low-and high-strength black water at a feed volume reduction up to 80%^90%.With an elevated feed pH(~9),approximately 60%-85%enriched phosphate-P was able to be recovered in the form of precipitated stuvite.Whereas the enrichment performance of total Kjeldahl nitrogen(TKN)largely differed depending on the strength of black water.Improved concentration factor(i.e.,3-folds)and retention(>60%)of TKN was obtained in the high-nutrient-strength black water at a feed volume reduction of 80%,in comparison with a weak TKN enrichment observed in low-strength black water.The results suggested a good potential for nutrient recovery based on this dual“waste-to-resource”FO system with proper management of membrane cleaning.