CO2 capture by membrane filtration is still an emerging technology, mainly due to low gas permeabilities and consequent poor separation efficiencies. Membrane-based processes offer lower material costs and operational simplicity and flexibility. Applications in pre-combustion and post-combustion have both been widely studied. For pre-combustion capture (CO2/H2 separation), H2 passes through the membrane to the other side (permeate side), leaving CO2 at the feed side, whereas in post-combustion capture (CO2/N2 separation), separation is achieved by CO2 preferentially passing through the membrane. Separation mechanisms are different depending on the membrane material and the gas stream, including: (1) size sieving, where the membrane's pore size is large enough to allow only the smaller gas molecule to pass through; (2) surface diffusion, where the surfaces of the membrane and pores are occupied by one gas through preferential adsorption, and become inaccessible to the other gas which therefore tends to stay at the feed side while the more adsorbable gas moves to the other side. (3) solution diffusion, where the more soluble gas preferentially dissolves into and then diffuses through the membrane. While the first two mechanisms work for porous membranes, the third occurs during separation using dense membranes. The most studied membranes can be classified into dense inorganic membranes, porous inorganic membranes, and polymer membranes, as summarized in Table . Most studied polymer membranes have been nonporous (dense) membranes. However, emerging materials such as conjugated microporous polymers, polymers of intrinsic microporosity, and thermally rearranged polymers, where pores with controlled architectures are introduced to organic polymers to improve CO2 permeability and CO2/N2 selectivity, have recently intrigued researchers. Polymer membrane matrices with inorganic fillers, combining the permeability and thermal stability of inorganic materials with mechanical strength and processability of polymers, have also shown promise. To further shed light on the status of development in CO2 capture and sequestration, we have also analyzed the prevalence and connections between different concepts occurring in related publications. The results are shown in Figure , where the size of a node reflects the number of times the corresponding concept occurred in the literature, lines between every two nodes denote co-occurrences in the same publication, and distances between nodes indicate the frequencies at which the concepts co-occurred. One interesting observation of the graph is that the concept "simulation and modeling" is in proximity to "absorption" and not "adsorption", the latter being instead adjacent to common adsorbent characterizations such as "pore size" and "surface structure". The relative material and operation simplicity for absorption capture likely explains the prevalence of its modeling studies.