Enhanced gas separation performance of polysulfone membrane by incorporation of zeolite-templated carbon

The zeolite-templated carbon (ZTC) with a unique structure was utilized as a new porous filler for preparing mixed matrix membrane (MMM). The zeolite-Y used as template was synthesized via hydrothermal method. The ZTC was prepared by impregnation of sucrose into the pore of zeolite-Y, followed by carbonization and template removal. The obtained ZTC was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2 isotherm analysis. Results showed that the ZTC was amorphous and possess specific surface area of 1254 m2/g and 0.95 cm3/g for total pore volume. The MMM was fabricated by adding 0.4 wt% ZTC via dry/wet spinning process with polysulfone (PSF) as the matrix. The fabricated membranes were analyzed using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM),and thermal gravimetric analysis (TGA), whereas the gas permeation properties weretested using single gases (CO2, O2, N2, CH4, and H2). The SEM results showed that incorporation of the ZTC was found to be similar as the morphological structure (dense layer and finger-like structure) of neat PSF membrane and the thermal stability was observed to be enhanced. In comparison to neat PSF membrane, uncoated PSF/ZTC MMM exhibited selectivities improvement for CO2/CH4 (290%), O2/N2 (117%), CO2/N2(219%) and H2/CH4 (272%), while coated PSF/ZTC MMM showed enhancement up to 1110%, 368%, 838%, and 802%, respectively with acceptable permeances. Compared to neat PSF membrane, profound selectivities enhancement could be achieved even with low ZTC loading inside the MMM

Multilayer composite polysulfone hollow fiber membrane modified by graphene oxide for gas separation

One of the most critical issues encountered by polymeric membranes for gas separation process is the trade-off effect between gas permeability and selectivity. The aim of this work is to develop a simple yet effective coating technique to modify the surface properties of commonly used polysulfone (PSF) hollow fiber membranes to address the trade-off challenge on CO2/CH4 and O2/N2 separation issue. More specifically, the first objective of this work is to study the effects of different types of PSF hollow fiber support on the gas separation performance of surface-coated membranes by varying significant imperative parameters, i.e., air gap (1–4 cm), dope extrusion rate (1–2 mL/min), bore fluid rate (0.33–0.67 mL/min) and polymer concentration (15–35 wt.%). Results showed that the support membrane spun at highest air gap of 4 cm and lowest dope extrusion rate at 1 mL/min were ideal for the coated membrane preparation owing to its good structural integrity that could produce a membrane with optimum balance composition for gas permeance and selectivity. The findings also revealed that the support membrane made of 25 wt.% PSF was the best for single layer coating and the membrane coated with polyether block amide (Pebax) performed better in terms of selectivity than the membrane coated with polydimethylsiloxane (PDMS) because Pebax solution tended to form denser layer as a result of its higher solution viscosity. However, the Pebax solution is prone to penetrate into the pores of support membrane, and thus lowering its permeability. Due to this, the second objective of this work is to investigate the efficiency of multilayer coating technique by forming Pebax (1–9 wt%) as selective outer layer and PDMS (3 wt%) as gutter layer on the PSF membrane surface. Results indicated that the optimized multilayer coated membrane at 3 wt% Pebax could achieve CO2/CH4 and O2/N2 selectivity of 35.19 and 6.56, respectively. As a comparison, the membrane coated with 1 wt% Pebax only showed 29.47 and 6.07, respectively. To further enhance the performance of multilayer coated membrane, the third objective of this work is to evaluate the impacts of graphene oxide (GO) loading from 0–1.0 wt% on the Pebax selective layer on the membrane performance. Experimental findings revealed that incorporating 0.8 wt% GO into the composites could further improve membrane performance, achieving selectivity as high as 52.57 and 8.05 for CO2/CH4 and O2/N2, respectively. This is due to formation of improved tortuous structure that created higher resistance to larger gas molecules (CH4 and N2) compared to smaller gas molecules (CO2 and O2). In conclusion, it can be said that the newly developed multilayer coating technique that combines polymeric materials and nanofillers could overcome the drawbacks of typical PSF membranes, producing a multilayer composite hollow fiber membrane with improved surface properties for gas separation

A green approach to modify surface properties of polyurethane foam for enhanced oil absorption

The non-selective property of conventional polyurethane (PU) foam tends to lower its oil absorption efficiency. To address this issue, we modified the surface properties of PU foam using a rapid solvent-free surface functionalization approach based on the chemical vapor deposition (CVD) method to establish an extremely thin yet uniform coating layer to improve foam performance. The PU foam was respectively functionalized using different monomers, i.e., perfluorodecyl acrylate (PFDA), 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA), and hexamethyldisiloxane (HMDSO), and the effect of deposition times (1, 5 and 10 min) on the properties of foam was investigated. The results showed that all the modified foams demonstrated a much higher water contact angle (i.e., greater hydrophobicity) and greater absorption capacities compared to the control PU foam. This is due to the presence of specific functional groups, e.g., fluorine (F) and silane (Si) in the modified PU foams. Of all, the PU/PHFBAi foam exhibited the highest absorption capacities, recording 66.68, 58.15, 53.70, and 58.38 g/g for chloroform, acetone, cyclohexane, and edible oil, respectively. These values were 39.19-119.31% higher than that of control foam. The promising performance of the PU/PHFBAi foam is due to the improved surface hydrophobicity attributed to the original perfluoroalkyl moieties of the HFBA monomer. The PU/PHFBAi foam also demonstrated a much more stable absorption performance compared to the control foam when both samples were reused for up to 10 cycles. This clearly indicates the positive impact of the proposed functionalization method in improving PU properties for oil absorption processes

Mixed matrix membranes incorporated with reduced graphene oxide (rGO) and zeolitic imidazole framework-8 (ZIF-8) nanofillers for gas separation

Mixed matrix membranes (MMMs) were successfully fabricated by incorporating reduced graphene oxide (rGO) and zeolitic imidazole framework-8 (ZIF-8) nanofillers into the polyethersulfone (PES) matrix. The synthesized nanofillers were characterized using XRD, FTIR, TGA and BET before being embedded into PES-based membranes. Their effects on the membrane morphology and gas separation performances at various operating pressure were studied. It was found that the addition of nanofillers led to a significant enhancement in gas permeabilities, particularly when a combination of rGO-ZIF-8 nanofillers was used. However, the CO2 and CH4 permeabilities for 2.0rGO-ZIF-8 MMMs were observed to decrease with increasing operating pressure. This work suggests that the formation of interface voids and membrane defects in the MMMs might lead to the high gas permeabilities and low gas selectivity. The membranes were then coated with polyether block amide (PEBAX) and the O2/N2 and CO2/CH4 selectivities were observed to improve significantly

Impacts of multilayer hybrid coating on PSF hollow fiber membrane for enhanced gas separation

One of the most critical issues encountered by polymeric membranes for the gas separation process is the trade-off effect between gas permeability and selectivity. The aim of this work is to develop a simple yet effective coating technique to modify the surface properties of commonly used polysulfone (PSF) hollow fiber membranes to address the trade-off effect for CO2 /CH4 and O2 /N2 separation. In this study, multilayer coated PSF hollow fibers were fabricated by incorporating a graphene oxide (GO) nanosheet into the selective coating layer made of polyether block amide (Pebax). In order to prevent the penetration of Pebax coating solution into the membrane substrate, a gutter layer of polydimethylsiloxane (PDMS) was formed between the substrate and Pebax layer. The impacts of GO loadings (0.0–1.0 wt%) on the Pebax layer properties and the membrane performances were then investigated. XPS data clearly showed the existence of GO in the membrane selective layer, and the higher the amount of GO incorporated the greater the sp2 hybridization state of carbon detected. In terms of coating layer morphology, increasing the GO amount only affected the membrane surface roughness without altering the entire coating layer thickness. Our findings indicated that the addition of 0.8 wt% GO into the Pebax coating layer could produce the best performing multilayer coated membrane, showing 56.1% and 20.9% enhancements in the CO2 /CH4 and O2 /N2 gas pair selectivities, respectively, in comparison to the membrane without GO incorporation. The improvement is due to the increased tortuous path in the selective layer, which created a higher resistance to the larger gas molecules (CH4 and N2 ) compared to the smaller gas molecules (CO2 and O2 ). The best performing membrane also demonstrated a lower degree of plasticization and a very stable performance over the entire 50-h operation, recording CO2 /CH4 and O2 /N2 gas pair selectivities of 52.57 (CO2 permeance: 28.08 GPU) and 8.05 (O2 permeance: 5.32 GPU), respectively

Separation of CO2/CH4 and O-2/N-2 by polysulfone hollow fiber membranes: effects of membrane support properties and surface coating materials

n this study, six different types of polysulfone hollow fiber membranes were fabricated from the same polymeric dope solution by manipulating several important parameters during the spinning process, aiming to find the best membrane supports for the coating layer in the gas separation process. The experimental results showed that upon the polydimethylsiloxane (PDMS) coating process, the gas pair selectivities of all six types of membranes were significantly increased with respect to carbon dioxide (CO2)/methane (CH4) and oxygen (O2)/nitrogen (N2) separation. However, the membrane support spun at higher air gap and lower dope extrusion rate was found to be the best support for PDMS coating owing to its good structural integrity that led to a good balance between gas permeance and gas pair selectivity. Further investigation showed that the use of poly(ether block amide) (Pebax) as coating material did not certainly improve both gas permeance and the selectivity of hollow fiber membranes, although Pebax was previously reported to exhibit better performance than PDMS in flat sheet membranes. One of the main reasons is the difficulty of forming a defect-free Pebax coating layer on the outer surface of hollow fibers owing to the stickiness issue among fibers upon coating. More research is still needed to optimize the Pebax coating solution and its drying process in order to achieve the full potential of such coating material for hollow fiber membranes