Scandium-Doped Nanosheets Push Carbon Capture to New Limits

Carbon capture has long been a story of compromise. Materials that soak up large quantities of carbon dioxide tend to grab everything else in the gas stream too, while materials that discriminate sharply in favor of CO2 often hold only modest amounts. A new computational study published in the Journal of Materials Science suggests that a two-dimensional carbon nitride nanosheet, chemically tuned with scandium atoms and mechanically tuned with strain, can push both dials at once — but only up to a point, and the trade-off between capacity and selectivity turns out to be exquisitely sensitive to how the material is engineered.

The research, led by Tiantian Qiao and Sainan Zhou of Liaoning University together with Xiaoqing Lu and Yongqing Li of the China University of Petroleum, focuses on C12N8, a porous single-layer carbon nitride framework. Using density functional theory calculations paired with grand canonical Monte Carlo simulations, the team systematically explored what happens when scandium atoms are incorporated into the lattice and when the sheet is stretched under tensile strain. Their central finding is that the two modification strategies play fundamentally different roles: doping is the dominant lever for performance, while strain acts as a secondary, double-edged adjustment.

The chemistry behind the improvement is electrostatic. When a scandium atom substitutes into the C12N8 framework, it behaves as a strong cationic center, withdrawing electron density from its surroundings and dramatically increasing the polarity of the nanosheet. Carbon dioxide, with its linear structure and pronounced quadrupole moment, is highly sensitive to such electric field gradients. The doped scandium sites become primary adsorption anchors, gripping CO2 molecules far more tightly than the pristine carbon nitride ever could. Nitrogen and methane, which lack the same charge distribution, feel a much weaker pull, and that asymmetry is what produces the material’s remarkable selectivity.

The numbers are striking. Under dry gas conditions at ambient temperature, unstrained Sc-doped C12N8 achieves a CO2/N2 selectivity of 369 and a CO2/CH4 selectivity of 468 — figures that place it among the best-performing adsorbents modeled to date for these industrially critical separations. Flue gas from power plants is dominated by nitrogen, and natural gas upgrading hinges on stripping CO2 from methane, so a material that discriminates this strongly against both contaminants addresses two of the largest separation problems in the energy economy simultaneously.

Capacity tells a complementary story. When the Sc-doped nanosheet is stretched by five percent, the simulated CO2 uptake reaches 8.19 millimoles per gram at 298 kelvin and 1 bar, conditions close to those of real post-combustion capture. Strain accomplishes this by reshaping the material’s geometry rather than its chemistry. Tensile deformation flattens the lattice topology and enlarges the accessible pore volume, giving CO2 molecules more room to pack inside the sheet. In effect, the stretched nanosheet becomes a roomier molecular warehouse, and the electrostatic anchors installed by scandium doping ensure that the additional guests are overwhelmingly carbon dioxide.

Yet the study’s most instructive result is what strain does not do — and what it costs. Applied to pristine C12N8, tensile strain alone delivers no improvement in CO2 uptake whatsoever; without the cationic anchors, extra pore volume is simply not enough. More importantly, in the doped system, strain boosts capacity at the expense of selectivity. The same flattening and pore expansion that lets more CO2 squeeze in also relaxes the geometric and energetic discrimination that made the unstrained material such a precise sieve. The highest selectivities belong to the unstrained doped sheet; the highest capacity belongs to the five-percent-stretched one. Engineers designing a real capture process would have to decide which figure matters more for their application, or find an intermediate strain that balances the two.

This capacity-selectivity trade-off is a recurring theme in adsorbent design, and the study frames it with unusual molecular-level clarity. Strong electrostatic interactions between open metal sites and CO2 drive both uptake and selectivity upward together, which is why scandium doping enhances both metrics. Strain, by contrast, is purely structural: it promotes CO2 packing but dilutes the selectivity advantage. The authors describe Sc-C12N8 as a promising two-dimensional molecular sieve, and the phrase is apt — the material’s performance depends on pore architecture and pore chemistry working in concert, and the simulations show precisely how each contribution can be dialed independently.

The choice of scandium is not arbitrary. The element sits among the transition metals known to form strong bonds with nitrogen, and prior work on scandium nitride films and Sc-embedded graphyne has highlighted its affinity for nitrogen-rich lattices. Embedding scandium in a carbon nitride framework therefore yields stable cationic sites rather than loosely bound decoration atoms that might cluster or leach. The study also builds on a body of earlier computational work by the same groups showing that alkali, alkaline earth, and first-row transition metal dopants can transform graphyne and covalent organic frameworks into high-performance CO2 sorbents, with the dopant’s charge and coordination environment governing how CO2 molecules arrange themselves in the pores.

Methodologically, the work illustrates the modern pipeline of adsorbent discovery. Density functional theory, with dispersion corrections to capture the weak van der Waals forces that dominate gas adsorption, provides the electronic structure and binding energetics; charge partitioning analysis quantifies the polarity that scandium introduces; and grand canonical Monte Carlo simulations using established force fields then translate those microscopic interactions into macroscopic adsorption isotherms and mixture selectivities at realistic temperatures and pressures. Because every step is computational, the results are predictions rather than measurements, but they define a concrete, testable target for synthetic chemists working on two-dimensional carbon nitrides, several of which have already been realized in the laboratory.

The broader significance lies in the design principle. Rather than searching blindly for a material that happens to capture CO2 well, the study demonstrates a modular strategy: choose a stable, porous two-dimensional framework, install cationic adsorption sites by doping, and then use lattice strain as a fine-tuning knob to trade capacity against selectivity as the application demands. As atmospheric CO2 concentrations continue to climb and carbon capture and storage moves from demonstration to deployment, materials that can be engineered at this level of precision — a single atomic layer, a single dopant species, a few percent of strain — may prove essential to making separation technology both effective and energy-efficient. The scandium-doped C12N8 nanosheet is a simulation today, but it is a simulation with a blueprint attached.

Subject of Research: Computational design of scandium-doped two-dimensional C12N8 nanosheets for CO2 capture and separation

Article Title: Balancing CO2 capture and selectivity through scandium doping and strain engineering in two-dimensional C12N8 nanosheets

Article References: Qiao, T., Zhou, S., Lu, X., & Li, Y. (2026). Balancing CO2 capture and selectivity through scandium doping and strain engineering in two-dimensional C12N8 nanosheets. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13796-4

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13796-4

Keywords: carbon capture, CO2 adsorption, two-dimensional materials, C12N8 nanosheets, scandium doping, strain engineering, density functional theory, grand canonical Monte Carlo, gas separation, molecular sieve, carbon nitride, selectivity