No abstract

Membrane gas absorption (MGA) is widely accepted for separating CO 2 from flue gas due to its superior advantages in overcoming the operational and economic issues encountered by conventional CO 2 removal technologies. However, the efficiency may reduce when the membrane starts to wet after the prolonged operation due to the invasion of liquid absorbent into the membrane pores. Therefore, the synthesis of the superhydrophobic membrane is of great significance to enhance the wetting resistance of the membrane. It can also ensure continuous process optimization. In this work, two PVDF membranes synthesized from polymers of different molecular weights (HMW/g-PVDF and LMW/g-PVDF) had first used to evaluate the wetting resistance. As shown by the characterization tests, the HMW/g-PVDF membrane demonstrated the most critical wetting issue because the WCA was lower at 92 , and the WCA had significantly reduced to 47 after the swelling evaluation. Since HMW/g-PVDF has the lowest wetting resistance, it had been used to synthesis superhydrophobic membranes by using templated substrate (non-woven fabric). The produced membranes were immersed in water or an ethanol coagulation bath and successfully printed hierarchical structures on the membrane surface. The change in the surface structure produced a higher surface roughness, reaching 4.4 μm, and exhibited a low contact angle hysteresis of 11.8 . The patterned membrane with excellent wetting resistance also showed a higher CO 2 absorption flux at 7.00 Â 10 À2 mol/m 2 s. This means that the hierarchical structure existing on the membrane surface played a significant role in overcoming the shortcomings of membrane wetting in MGA.

No abstract

The severe water pollution from effluent dyes threatens human health. This study created pH-magnetic-photocatalytic polymer microspheres to conveniently separate the photocatalyst nanoparticles from the treated water by applying an external magnetic field. While fabricating magnetic nanoparticles’ (MNPs) microspheres, incorporating 0.5 wt.% iron oxide (Fe3O4) showed the best magnetophoretic separation ability, as all the MNPs microspheres were attracted toward the external magnet. Subsequently, hybrid organic–inorganic polyoxometalates (HPOM), a self-synthesized photocatalyst, were linked with the functionalized magnetic nanoparticles (f-MNPs) to prepare augmented magnetic-photocatalytic microspheres. The photodegradation dye removal efficiency of the augmented magnetic-photocatalytic microspheres (f-MNPs-HPOM) was then compared with that of the commercial titanium dioxide (TiO2) photocatalyst (f-MNPs-TiO2). Results showed that f-MNPs-HPOM microspheres with 74 ± 0.7% photocatalytic removal efficiency better degraded methylene orange (MO) than f-MNPs-TiO2 (70 ± 0.8%) at an unadjusted pH under UV-light irradiation for 90 min. The excellent performance was mainly attributed to the lower band-gap energy of HPOM (2.65 eV), which required lower energy to be photoactivated under UV light. The f-MNPs-HPOM microspheres demonstrated excellent reusability and stability in the photo-decolorization of MO, as the microspheres retained nearly the same removal percentage throughout the three continuous cycles. The degradation rate was also found to follow the pseudo-first-order kinetics. Furthermore, f-MNPs-HPOM microspheres were pH-responsive in the photodegradation of MO and methylene blue (MB) at pH 3 (acidic) and pH 9 (alkaline). Overall, it was demonstrated that using HPOM photocatalysts in the preparation of magnetic-photocatalytic microspheres resulted in better dye degradation than TiO2 photocatalysts.

Membrane gas absorption (MGA) as an emerging technology exhibits superior advantages in comparison to conventional carbon dioxide (CO2) absorption processes. However, the decrease in membrane flux, induced by membrane wetting is a significant issue to be pondered upon. Thus, fabrication of an anti-wetting composite membrane is essential to retain and sustain the MGA performance. In this work, silica nanoparticles (SiNPs) is first coated with hydrophobic low-density polyethylene (LDPE). Then, integrating LDPE-HMDS/SiNPs fillers into the polyvinylidene fluoride (PVDF) matrix to increase its hydrophobicity. The incorporation of LDPE-coated silica into PVDF polymer enhanced the contact angle values from 71.8° to 111.8°, indicates the improvement of membrane anti-wetting ability. Despite the similar finger-like layer laid on top of the sponge-like structure for pristine and composite membranes, the incorporation of LDPE-HMDS/SiNPs has reduced in the length ratio of finger-like to sponge-like layer. The changed in the membrane morphology induced higher membrane hydrophobicity which prevent membrane from getting wet easily especially in long term of operation. In addition, EDX surface mapping and lining profiles clearly proved that the LDPE-HMDS/SiNPs were distributed evenly in the composite membranes indicates the good interfacial compatibility between PVDF polymer and LDPE-coated silica. In term of CO2 absorption flux, the embedment of LDPE-HMDS/SiNPs in PVDF polymer matrix demonstrated 2.4x10-3 mol/m2.s which was 2 times higher than that of the pristine membrane. This means the incorporation of LDPE-HMDS/SiNPs into the PVDF membrane has still played a pivotal role in overcoming membrane wetting drawbacks when in contact with the liquid absorbents.