Nik Abdul Hadi Md Nordin

The impact of ZIF-8 particle size and heat treatment on CO2/CH4 separation using asymmetric mixed matrix membrane

In this study, zeolitic imidazole framework 8 (ZIF-8) particles of different sizes were synthesized in aqueous media by varying the concentration of the base-type additive, triethylamine (TEA). ZIF-8 with particle sizes of ∼134 nm and ∼288 nm with surface areas of 418.44 m2 g−1 and 491.54 m2 g−1 were obtained without altering the crystalline structure. Synthesized ZIF-8 was further heat treated at 100 °C for a minimum of 12 hours, which led to an enhancement of its phase crystallinity and a surface area of 981.1 m2 g−1. Mixed matrix membranes (MMMs) were prepared via the dry–wet phase inversion method by dispersing as-synthesized ZIF-8s, heat-treated ZIF-8s and commercial ZIF-8 (∼493 nm) into a polysulfone (PSf) matrix. The thermal stability and mechanical strength of the membranes showed significant improvement after the incorporation of ZIF-8s. The MMMs were further subjected to the permeation experiments of CO2 and CH4. Although the majority of MMMs showed less selectivity than the neat PSf membrane, the incorporation of heat-treated ZIF-8 of the smallest size, exhibited CO2/CH4 selectivity of 28.5, which is significantly higher than the 19.43 obtained for the neat PSf membrane. Therefore, different ZIF-8 treatment protocols and particle sizes affect the MMMs performance significantly.

Aqueous room temperature synthesis of zeolitic imidazole framework 8 (ZIF-8) with various concentrations of triethylamine

In this study, a zeolitic imidazole framework (ZIF-8) was prepared, and physico-chemical characterizations were performed to investigate the influences of triethylamine (TEA) on the crystallinity, particle size, morphology, and defects of ZIF-8 synthesized via an aqueous room temperature approach with a relatively low molar ratio of ligands to metal salts. Increasing the concentration of TEA by raising the TEA/total molar ratio from 0.004 to 0.007 prompted the formation of pure phase ZIF-8, whereas a TEA/total molar ratio below 0.004 did not result in a yield of ZIF-8. The particle size of ZIF-8 decreased from approximately 288 to 133 nm with increasing TEA/total molar ratio, except at a TEA/total molar ratio of 0.007. However, an excessive TEA/total molar ratio alters the 2-MeIM chemistry, and partially forms hydroxylated 2-MeIM. Thus, this study shows that at relatively low molar ratios of ligands to metal salts, up to a maximum TEA/total molar ratio of 0.006, the TEA concentration plays an important role in assisting crystal formation and in controlling the particle size of ZIF-8. The proposed procedure enables pure phase nanoscale ZIF-8 to be synthesized with a high product yield and with minimal chemical usage.

Facile modification of ZIF-8 mixed matrix membrane for CO2/CH4 separation: synthesis and preparation

Metal–organic frameworks (MOFs) possess tunable characteristics that allow various modifications to be practiced and suitability for specific applications. In this study, zeolitic imidazole framework 8 (ZIF-8) was synthesized and subjected to ammonia modification under different temperatures and ammonia solution loading. The presence of the N–H group observed after the modification indicates the successful modification of ZIF-8. The modified ZIF-8 showed notable changes with increased phase crystallinity, micropore volume and BET surface area. The unmodified and modified ZIF-8s were then dispersed into a polysulfone (PSf) matrix, and the MMMs were prepared via dry/wet phase inversion. No apparent differences in the membrane’s morphology and thermal stability were noticed between the neat PSf membrane and the MMMs. The MMMs were further subjected to pure CO2 and CH4 gas permeation experiments. CO2 permeance decreased while CO2/CH4 selectivity increased as a result of ZIF-8 modification, due to the decrease in mesopore contribution and the increase in micropore contribution to the gas permeation path. The affinity of the N–H group in the modified ZIF-8 to CO2 also contributed to the increase of CO2 permeance. For example, when the ZIF-8 modified in 25 mL ammonia solution at 60 °C (Z25c) was dispersed in the PSf matrix, the CO2/CH4 selectivity increased to 72% and CO2 permeability to 43% compared to the neat PSf membrane.

Utilizing low ZIF-8 loading for an asymmetric PSf/ZIF-8 mixed matrix membrane for CO2/CH4 separation

Asymmetric mixed-matrix membranes (MMMs) were synthesized by incorporating zeolitic imidazole framework 8 (ZIF-8) into polysulfone (PSf) polymer matrix for CO2/CH4 separation. ZIF-8 was synthesized in aqueous media at room temperature with a base-type additive, triethylamine (TEA). The prepared ZIF-8 shows high crystallinity with a surface area of 1032 m2 g−1 and a particle size of ∼133 nm. MMMs were then prepared by incorporating the synthesized ZIF-8 up to 10 wt% (total solids) into PSf via a dry/wet phase inversion. The prepared MMMs exhibit significant improvement in thermal and mechanical stability even at a filler loading as low as 0.25 wt%. Uniform dispersion of ZIF-8 throughout the PSf matrix was evident via SEM, up to 1 wt% filler loading. The permeation behavior of MMMs varies with the ZIF-8 loading; i.e. insignificant change was observed at the low filler loading (0.25 wt%), while severe performance deterioration occurred at high filler loading (10 wt%). At an optimal ZIF-8 loading of 0.5 wt%, CO2 permeance was enhanced by 37% and CO2/CH4 selectivity was also enhanced by 19% as compared to that of neat PSf membrane.

Enhanced carbon dioxide separation by polyethersulfone (PES) mixed matrix membranes deposited with clay

Abstract Asymmetric mixed matrix membranes (MMMs) incorporating Cloisite15A (C15A) clay particles were prepared using solvent evaporation and phase inversion with polyethersulfone (PES) as the membrane matrix. C15A loadings varied at 1 wt% and 5 wt%. Membrane morphological and thermal properties were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Addition of the C15A favorably altered the microscopic structure of membranes from finger-like to homogeneous sponge-like structure as the loading increased. While the amorphous nature of MMMs was retained, the thermal stability was also found to be improved with a slight decrease in glass transition temperature (Tg). PES/C15A1 MMM showed the best gas transport properties, with 37% and 65% improvement in CO2 permeance and CO2/CH4 selectivity, respectively. Unlike 1 wt%, the loss in selectivity shown by 5 wt% clay loadings suggested that the interphase voids and extent of silicate layers dispersion play a significant role in the overall performance of MMMs.

Modified ZIF-8 mixed matrix membrane for CO2/CH4 separation

Tunability of metal–organic frameworks (MOFs) properties enables them to be tailored for specific applications. In this study, zeolitic imidazole framework 8 (ZIF-8), sub-class of MOF, underwent pre-synthesis and post-synthesis modifications. The pre-synthesis modification using GO (ZIF-8/GO) shows slight decrease in textural properties, while the post-synthesis modification using amine solution (ZIF-8/NH2) resulted in superior BET surface area and pore volume. Mixed matrix membranes (MMMs) derived from polysulfone (PSf) and the modified ZIF-8s were then prepared via dry/wet phase inversion. The polymer chain flexibility of the resulted MMMs shows rigidification, where ZIF-8/NH2 as filler resulting higher rigidification compared to ZIF-8/GO. The MMMs were further subjected to pure CO2 and CH4 gas permeation experiments. The PSf/ZIF-8/NH2 shows superior CO2/CH4 selectivity (88% increased) while sacrificing CO2 permeance due to combination of severe polymer chain rigidification and the presence of CO2-phili...

Influence of carbonisation temperature on gas permeation properties of matrimid-based carbon membrane

The utilisation of tubular support for carbon membrane preparation is beneficial for gas separation by providing high membrane area per unit volume and mechanically stronger than conventional flat substrate. In this study, tubular carbon membrane derived from Matrimid was fabricated via dip-coating method and three different carbonisation temperatures were used in order to produce high performance carbon membrane (600 °C, 750 °C and 850 °C). The physicochemical property of the carbon membrane is highly dependent on the final carbonisation temperature. By increasing carbonisation temperature, it will result in higher micropores and increasing gas pair selectivity. Whereas, low carbonisation temperature constricts pore formation and resulting in lower gas separation properties. The carbon membrane carbonised at 850 °C showed the highest gas separation properties of CO2/CH4 selectivity of 87.30 with CO2 permeance of 287.36 GPU. The resulted membrane is compared with literatures and has highlighted the potential of carbon tubular membrane for future membrane development.