Stability Of Polymeric Membranes Research Articles

Investigation of Structural Stability for Monolithic Nano Bridges on Micro Apertures

The instability of polymeric membranes with nano- and micro-sized apertures has been regarded as one of the main reasons behind realizing ultra-thin membranes with apertures. As is well known, when the thickness of the membrane gets thinner or the aperture size gets smaller, the possibility of geometrical deformation or structural damage by collapse or fracture increases. Herein, we suggest the design rules for the stability of polymeric membranes possessing 1D nano-line patterns monolithically constructed on micro-aperture supporting layers. The proposed theoretical model, which has been thoroughly demonstrated and analyzed based on both theoretical and experimental approaches, provides stability criteria for lateral collapse and vertical fracture of ultra-thin membranes with apertures.

Humic acid fouling in a submerged photocatalytic membrane reactor with binary TiO2–ZrO2 particles

The binary TiO2–ZrO2 particles were better alternative to TiO2 particles as photocatalyst to reduce humic acid fouling in photocatalytic membrane reactor. The structure of the TiO2–ZrO2 particles was strongly dependent upon the content of zirconium as an additive. A composition of 50% TiO2 with 50% ZrO2 was optimal in terms of physicochemical properties. The effect of TiO2–ZrO2 particles on the reduction of humic acid fouling was further improved by the presence of divalent cations such as calcium. Nevertheless, the stability of polymeric membranes in longer-term operation using a hybrid photocatalytic membrane reactor for water treatment applications may remain a challenge.

A molecular investigation of the nanostructure and dynamics of phosphoric–triflic acid blends of hydrated ABPBI [poly(2,5-benzimidazole)] polymer electrolyte membranes

Poly(2,5-benzimidazole) membranes (ABPBI) doped with phosphoric acid (PA) are known to serve as promising electrolytes in fuel cells. The addition of triflic acid, which exist in its dissociated form (TFA), is known to enhance the efficiency of PA-doped ABPBI membranes. In the present work, we employ classical molecular dynamic simulations to characterize the structure and dynamics of ABPBI + PA, ABPBI + TFA and ABPBI + PA + TFA blends with varying levels of hydration. The structural properties seen from the radial distribution functions (RDFs) show that the distance between two adjacent imidazole units on the polymer chain remain unaffected by hydration and the type of blend. The end-to-end polymer chain distance and radius of gyration are also unaffected by hydration and the type of blend, illustrating that the stability of polymer membranes under various hydrated acidic environments remains unaffected. The number of PA, TFA and water molecules in the cluster around the polymer membrane (skewed and extended form) is found to depend significantly on the extent of hydration. The lowest water mobility was obtained from the ABPBI + PA + TFA blend, which suggests that this blend could be the most effective in reducing acid leaching from the membrane matrix.

The stability of polymeric membranes in a TiO 2 photocatalysis process

The coupling of photocatalysis with membrane separation has emerged as a promising water treatment process. This study focuses on the selection of polymeric membranes for the photocatalytic-membrane process. Ten membranes were evaluated under ultraviolet (UV) and TiO 2 photocatalysis conditions. Membrane stability was characterized by changes in pure water flux (PWF), release of total organic carbon (TOC) and scanning electron microscope (SEM) morphology analysis. The results revealed that polytetrafluoroethylene (PTFE), hydrophobic polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN) membranes showed the greatest stability. However, in a study of the oxidative stability of membranes, it was found that the PAN membrane is not suitable to be exposed to 10 days of 200 mM H 2O 2/UV conditions. Tests with cross-flow filtration conditions to prevent titanium dioxide (TiO 2) cake formation were carried out. It was shown that during the non-cake situation, TiO 2 deposition was minimized at appropriate pH values and this reduced membrane deterioration. Deposition of cakes with various thicknesses of TiO 2 affected the stability of the membranes to different extents. In general, the thicker the cake layer, the less the damage done by the photocatalytic reaction on the membrane. Chemical changes on the membrane surface after the TiO 2 cake studies were characterized using attenuated total reflection-Fourier transform infrared (ATR-FTIR). The results obtained using powdered activated carbon (PAC) as a separating layer showed that close contact between the TiO 2 and the membranes was the main mechanism for the detrimental effect of TiO 2 on polymeric membrane exposed to UV light.