Silanization of magnetic ironoxide nanoparticles with (3-aminopropyl)triethoxylsilane (APTES) is reported. The kinetics of silanization toward saturation was investigated using different solvents including water, water/ethanol (1/1), and toluene/methanol (1/1) at different reaction temperature with different APTES loading. The nanoparticles were characterized by Fourier transform infrared spectroscopy, vibrating sample magnetometry, transmission electron microscopy, and thermal gravimetric analysis (TGA). Grafting density data based on TGA were used for the kinetic modeling. It is shown that initial silanization takes place very fast but the progress toward saturation is very slow, and the mechanism may involve adsorption, chemical sorption, and chemical diffusion processes. The highest equilibrium grafting density of 301 mg/g was yielded when using toluene/methanol mixture as the solvent at a reaction temperature of 70 °C.

•Co-casting of PSf on top of PEI to form the supporting layer was demonstrated.•Delamination of PSf from PEI yielded a porous penetration-through supporting layer.•TFC FO membranes from co- and single-casting supporting layer were compared.•Support layer from co-casting had lower S value than that from single layer casting.•Compared to single layer casting, co-casting membranes showed notably lower ICP.This study demonstrates a sacrificial-layer approach by co-casting, which is the simultaneous casting of two layers, to prepare a polysulfone support (denoted as PSfco) layer with open bottom surface morphology for fabricating thin-film composite forward osmosis (FO) membranes. In the co-casting process, polyetherimide (PEI), used as the sacrificial layer, was co-cast beneath the PSf layer. After the PEI layer was peeled off, PSfco was yielded with an open-bottom structure. Results showed that under the same operating condition, the FO membrane prepared by co-casting (denoted as PSfco-TFC) demonstrated a 10% higher water flux using 0.5 M NaCl draw solution and 30% higher water flux using 4 M NaCl draw solution in the AL-FS mode in comparison to membranes prepared in a single layer casting technique (denoted as PSfs-TFC). The PSfco-TFC exhibits a lower average structural parameter (S, 167 μm) than that of the PSfs-TFC (241 μm), while the water and salt permeability coefficients of both membranes are similar. Results reported here demonstrate that the co-casting technique can be used to fabricate FO membranes with significantly improved performance compared to the conventional approach.

•Surface hydrophobicity contribution to the MD flux was evaluated.•An effective evaporation factor, φ, was introduced in modeling MD flux.•The parameter, φ, is determined by the surface hydrophobicity and porosity.•A high φ value corresponds to a high evaporation efficiency.PVDF membranes, after surface modification by CF4 plasma, have demonstrated surperhydrophobic surface characteristics and up to 30% flux enhancement in direct contact membrane distillation (MD). The heat transport in the MD process was modeled to assess the membrane distillation coefficients (Bm). The experimentally determined Bm showed up to 50% deviation from the modeled values for CF4 modified PVDF membranes. An effective evaporation factor, as a function of surface porosity and surface water contact angle, was proposed to correlate surface wettability contribution to the MD flux. This factor was fitted by comparing the experimentally determined flux with modeled one. It was found that the factor, which is positively related to surface water contact angle and surface porosity, varied with the membrane wettability and can rationally explain the deviation between observed and theoretical fluxes. In addition, CF4 plasma modification could increase the membrane׳s evaporation efficiency from 54.3% for the virgin membrane up to 63.4% for surface modified membranes because of the increase of the effective evaporation area factor. The introduction of the factor provides a means to evaluate the membrane surface hydrophobicity to the MD flux and necessitate the development of super even ultra-hydrophobic membranes.

A new composite hollow fiber nanofiltration (NF) membrane with a thin sulfonated poly(ether ether ketone) (SPEEK) active layer was prepared and used for arsenic removal. The effects of the feed concentration, pH and transmembrane pressure on arsenic removal were systematically examined. The obtained SPEEK hollow fiber NF membrane could achieve an As(V) rejection of over 95% and water permeability of 11 L m−2 h−1 bar−1. These excellent As(V) rejection and high water permeability were attributed to the highly negatively charged surface of the SPEEK membrane, which could enhance the As(V) rejection through the Donnan exclusion mechanism or electrostatic repulsion between the negatively charged arsenate species and the negatively charged SPEEK membrane surface. A preliminary techno-economic assessment of a 1000 m3 h−1 plant suggests that using the proposed SPEEK hollow fiber membrane, the treatment cost was 0.15 US$ per m3, which thus could be economically viable for arsenic removal applications in China.

Stability of supported liquid membrane (SLM) has been a key issue in the application of high efficiency liquid membranes. In this paper, a nanoporous ion exchange membrane, prepared by blending polyethersulfone (PES) with sulfonated poly (phenyl ether ketone, SPPESK), was utilized as the stabilizing barrier for the extraction of lithium ion based on liquid–liquid membrane extraction. The membrane was prepared via immersion precipitation and the ratio between PES and SPPESK was varied in order to obtain a membrane with the best performance. It was found that at a PES/SPPESK ratio of 6/4 and a polymer concentration of 30 wt%, the membrane showed a Li+ flux of 1.67×10−8 mol cm−2 s−1 at a Li+ feed concentration of 0.13 mol/L. The membrane demonstrated nearly unchanged stress but a slight decline in elongation after 50 days in contact with the organic extractant, indicating the potential solvent resistance. Using tributylphosphate (TBP) as the extractant and kerosene as the diluent, lithium extraction and stripping were demonstrated in both single-staged and sandwiched membrane extraction contactor systems. The preliminary results on using SPPESK/PES barrier membrane for stabilizing the liquid membrane will lead to a new scientific and technology development in lithium mining from brine and seawater in the near future.

Silanization of magnetic ironoxide nanoparticles with (3-aminopropyl)triethoxylsilane (APTES) is reported. The kinetics of silanization toward saturation was investigated using different solvents including water, water/ethanol (1/1), and toluene/methanol (1/1) at different reaction temperature with different APTES loading. The nanoparticles were characterized by Fourier transform infrared spectroscopy, vibrating sample magnetometry, transmission electron microscopy, and thermal gravimetric analysis (TGA). Grafting density data based on TGA were used for the kinetic modeling. It is shown that initial silanization takes place very fast but the progress toward saturation is very slow, and the mechanism may involve adsorption, chemical sorption, and chemical diffusion processes. The highest equilibrium grafting density of 301 mg/g was yielded when using toluene/methanol mixture as the solvent at a reaction temperature of 70 °C.

•Dual-bath coagulation process yielded membranes with highly open surface.•Surface hydrophobicization was achieved by CF4 plasma modification.•PSf membranes showed as twice as high a MD flux as that of PVDF membranes.•Heat and mass simulation revealed a low tortuosity for PSf membranes.Preparation of MD membranes with a low tortuosity and high DCMD flux is reported. Hydrophilic flat sheet polysulfone (PSf), blended with polyvinylpyrrolidone (PVP) membranes were prepared by dual-bath coagulation phase inversion, where N-methylpyrrolidone (NMP)/water mixtures were used as the first coagulant before immersion into a water bath. CF4 plasma modification was utilized to render the originally hydrophilic membranes hydrophobic. The membranes were characterized by scanning electron microscopy (SEM), water contact angle, X-ray photoelectron spectroscopy (XPS), liquid entry pressure (LEPw), and gas permeability. Results demonstrated that the first coagulation bath acted as a dense skin layer remover in comparison to a PSf membrane prepared in a single water bath. CF4 plasma modified porous PSf membranes using pure NMP as the first coagulant showed a contact angle of 144° and a DCMD flux of 53.33 kg/m2 · h (Tf = 70.3 °C), which was 80% higher than a commercial PVDF membrane with comparable performance stability. Heat and mass simulation modeling results demonstrated that the tortuosity of the PSf membranes is close to 1 in contrast to 2.5 for the commercial PVDF membranes. This result provides some theoretical understanding of the origin of the high performance of PSf MD membranes.Download full-size image

•TFC FO membrane outperformed CTA membrane in treating synthetic brine.•Severe fouling was found for TFC FO membrane in treating SGDF.•No significant fouling was found for CTA FO membrane in treating SGDF.•Ultrafiltration pretreatment only delays fouling formation of TFC membrane.•PEG grafting to the TFC membrane alleviates membrane fouling.A polyamide thin-film composite (TFC) forward osmosis (FO) membrane was fabricated and compared to a commercially available cellulose acetate (CTA) membrane for treating shale gas drilling flow-back fluids (SGDFs). The polyamide TFC membrane outperformed its CTA counterpart in terms of pure water flux and reverse salt flux when synthetic brine was used as the feed. More severe fouling was observed for the polyamide TFC membrane as compared to the CTA counterpart when treating SGDF. Very quick buildup of fouling was identified for TFC membrane but not significant for CTA membrane. Ultrafiltration pre-treatment delayed but did not alleviate fouling formation. Surface modification of the TFC membrane by poly(ethylene gycol) (PEG) grafting resulted in reduced membrane fouling and marginal decrease in water flux.

•Origin of instability of SPEEK nanofiltration membranes is revealed.•Reptation rate of polymer chains determines membrane rejection.•Stable performance for SPEEK-PVA cross-linked membrane over 2000 h was obtained.•Constraints help to reduce the loss rate of SPEEK.Composite hollow fiber nanofiltration membrane coated with a thin layer of sulfonated poly(ether ether ketone) (SPEEK) can separate monovalent ions from multivalent ions with a low energy demand. It has found applications in desalination of glyphosate wastewater and removal of arsenic from drinking water. Before large scale application of such membranes, one of the main issues is the long time performance stability. This paper reports, for the first time, systematic investigations on the origins of the instability of the SPEEK composite membrane in aqueous phase. Membrane preparation parameters, the coating polymer concentration, the coating time, and the post-treatment temperature were correlated to the membrane stability. A reptation mechanism was proposed to explain the rejection decline and flux increase with time, based on swelling and dissolution of SPEEK. To reduce the swelling and loss of SPEEK, a PVA/SPEEK blend was used as the coating layer, which after cross-linking by glutaraldehyde, yielded a NF membrane with constant rejection during 2000 h of operation.Download full-size image

A new composite hollow fiber nanofiltration (NF) membrane with a thin sulfonated poly(ether ether ketone) (SPEEK) active layer was prepared and used for arsenic removal. The effects of the feed concentration, pH and transmembrane pressure on arsenic removal were systematically examined. The obtained SPEEK hollow fiber NF membrane could achieve an As(V) rejection of over 95% and water permeability of 11 L m−2 h−1 bar−1. These excellent As(V) rejection and high water permeability were attributed to the highly negatively charged surface of the SPEEK membrane, which could enhance the As(V) rejection through the Donnan exclusion mechanism or electrostatic repulsion between the negatively charged arsenate species and the negatively charged SPEEK membrane surface. A preliminary techno-economic assessment of a 1000 m3 h−1 plant suggests that using the proposed SPEEK hollow fiber membrane, the treatment cost was 0.15 US$ per m3, which thus could be economically viable for arsenic removal applications in China.