Multipulsed Millisecond Ozone Gasification for Predictable Tuning of Nucleation and Nucleation-Decoupled Nanopore Expansion in Graphene for Carbon Capture

Abstract

Predictable and tunable etching of angstrom-scale nanopores in single-layer graphene (SLG) can allow one to realize high-performance gas separation even from similar-sized molecules. We advance toward this goal by developing two etching regimes for SLG where the incorporation of angstrom-scale vacancy defects can be controlled. We screen several exposure profiles for the etchant, controlled by a multipulse millisecond treatment, using a mathematical model predicting the nucleation and pore expansion rates. The screened profiles yield a narrow pore-size-distribution (PSD) with a majority of defects smaller than missing 16 carbon atoms, suitable for CO 2 /N 2 separation, attributing to the reduced pore expansion rate at a high pore density. Resulting nanoporous SLG (N-SLG) membranes yield attractive CO 2 permeance of 4400 ± 2070 GPU and CO 2 /N 2 selectivity of 33.4 ± 7.9. In the second etching regime, by limiting the supply of the etchant, the nanopores are allowed to expand while suppressing the nucleation events. Extremely attractive carbon capture performance marked with CO 2 permeance of 8730 GPU, and CO 2 /N 2 selectivity of 33.4 is obtained when CO 2 -selective polymeric chains are functionalized on the expanded nanopores. We show that the etching strategy is uniform and scalable by successfully fabricating high-performance centimeter-scale membrane.

Gas Separations using Nanoporous Atomically Thin Membranes: Recent Theoretical, Simulation, and Experimental Advances

“…Compilation of experimentally measured H 2 /CH 4 and CO 2 /N 2 separation performances by NATMs in a selectivity‐permeance Robeson plot. The experimental results are categorized according to the perforation methods used, including ion beam bombardment (some followed by additional chemical etching), [ 150–154,156,157 ] oxidative etching, [ 143,158–166 ] and intrinsic defect formation during CVD. [ 62,143,149,159,160,164,167–171 ] The Robeson upper bounds for polymers are plotted assuming 1 µm thickness.…”

“…[143,160] Since then, O 3 and oxygen plasma treatment have been frequently reported to nucleate and expand pores in NATMs. [158,162,[164][165][166] Because these oxidative etchants can participate in both pore nucleation and pore expansion, the coupling between the two processes and the subsequent wide PSD have become a concern. To address this challenge, Zhao et al developed a two-step procedure as follows.…”

“…Note that this prediction is based on the assumption that pore nucleation is temporally uniform (Equation ( 18)). If the etchant concentration changes over time, [165,166] the resulting PSD also depends on the concentration profile of the etchant.…”

“…[163] Hsu et al claim that the energy barriers for nanopore nucleation and expansion are similar for O 3 (≈1 eV), which increases r nuc /r according to Equation (22) and yields a higher pore density and higher gas permeances. [165] In spite of the strategy discussed above, pore nucleation triggered by oxidative etching cannot be completely decoupled from pore expansion. Ion bombardment and intrinsic defect formation are two alternative methods that may better enable the decoupling.…”

“…Figure 6. Compilation of experimentally measured H 2 /CH 4 and CO 2 /N 2 separation performances by NATMs in a selectivity-permeance Robeson plot.The experimental results are categorized according to the perforation methods used, including ion beam bombardment (some followed by additional chemical etching),[150][151][152][153][154]156,157] oxidative etching,[143,[158][159][160][161][162][163][164][165][166] and intrinsic defect formation during CVD [62,143,149,159,160,164,[167][168][169][170][171]. The Robeson upper bounds for polymers are plotted assuming 1 µm thickness [11].…”