Shaping nanofiltration channels in a carbonaceous membrane via controlling the pyrolysis atmosphere

Abstract

This work investigates the effect of atmosphere on pyrolysis of a polymer matrix (precursor) for directing its transformation towards more disordered graphene species and smaller graphitic nanograins. These two structural characteristics are crucial to the generation of nano-channels (NCs) pertinent to nanofiltration (NF). Two measures are explored hereby to conduct the study: varying the pyrolysis atmosphere and implementing highly dispersed nickel atomic clusters (Ni-clusters) in the coating matrix undergoing pyrolysis. A thermally reactive polymer precursor is developed to allow the above two measures to act more effectively. The various pyrolysis atmospheres employed include inert Ar, a reducing H/N gas mixture, and weak oxidizing CO. In the absence of the Ni-clusters, the H/N atmosphere restrains the extent of graphitization through a chain transfer effect of H that ceases the free radical chain propagation, whereas CO, owing to its high critical temperature (T) nature, shows the capability to reduce nanograin sizes. As for the catalytic roles of the embedded Ni-clusters, they vary with the pyrolysis atmosphere applied: offering coke nuclei for the growth of carbonaceous grains in Ar, enhancing gasification of carbon in CO, and repressing the extent of aromatization via hydrogenation in H/N. The carbonaceous membranes (CnMs) obtained under the above pyrolysis conditions are distinguished by the distribution density and structure of NCs evolved, which locate primarily in the boundaries of nanograins. The NF of an aqueous solution of methylene blue (MB, 10 ppmw) is utilized to assess these CnMs to show impacts of the NCs on the separation performance.

Strategy to Chemically Decorate Nanopores of a Carbon Membrane for Filtrating Polyphenolics from Ethanol

“…Asphaltene has a PAH core surrounded by paraffin side chains and naphthenes . This special molecular structure intends to aggregate and form nano aromatic clusters through dehydrogenation and a successive cyclization process upon pyrolysis, − which leaves behind a core-boundary carbon pattern (Figure ). This is because the PAH core is much less vulnerable to heat than the peripheric aliphatic chains.…”

“…This is because the PAH core is much less vulnerable to heat than the peripheric aliphatic chains. Besides, the side aliphatic chains undergo a series of elimination and dehydrocyclization processes to form aromatic naphthenic bridges amidst stacked aromatics under an inert atmosphere . This study conducted pyrolysis of the bitumen coating on porous stainless-steel disk (PSD) in Ar and set the highest calcination temperature at 500 °C.…”

“…Besides, the side aliphatic chains undergo a series of elimination and dehydrocyclization processes to form aromatic naphthenic bridges amidst stacked aromatics under an inert atmosphere. 41 This study conducted pyrolysis of the bitumen coating on porous stainless-steel disk (PSD) in Ar and set the highest calcination temperature at 500 °C. Conducting carbonization at a relatively lower temperature with respect to the usual range (700−900 °C) allows a low graphitization extent, so that a low tap density (∼1.79 g/cm 3 ) compared to the amorphous carbon density (2.25 g/cm 3 ) 42 is attained.…”