Tiny Crystal Pores Trigger Selective CO₂ and Benzene Recognition

Researchers from Shibaura Institute of Technology develop an adaptive crystal that selectively captures CO₂ and recognizes similar molecules

Chemical separation can be energy-intensive when molecules have similar sizes and properties. Researchers from Shibaura Institute of Technology, Japan, developed an interlayer adaptive crystal that changes its spacing to recognize specific molecules. The crystal showed appreciable CO₂ uptake at pressures as low as 2.0 Pa (195 K) and selectively separated CO₂ from nitrogen and methane at 303 K, even under highly humid conditions. It also preferentially captured benzene over several similar molecules, offering a new approach to molecular separation.

Chemical separation is among the most energy-intensive operations in modern industry, with separation processes such as distillation estimated to account for approximately 10–15% of global energy consumption, creating a need for efficient approaches to carbon capture and purification. Conventional porous materials often rely on pore size and adsorption strength, which can struggle to distinguish molecules with similar dimensions. The researchers therefore explored whether a crystal could adapt its internal space to incoming molecules.

Addressing this challenge, a research team led by Professor Akiko Hori, together with graduate students Masahiro Abe and Tomoki Jitsukata from Shibaura Institute of Technology, Japan, and Professor Ryotaro Matsuda from Nagoya University, Japan, developed an interlayer adaptive crystal (LAC). The material is made of thin layers that can move apart when certain molecules approach. Their findings were published in the journal Angewandte Chemie International Edition on August 24, 2026.

“Rather than relying only on molecular size, we focused on the characteristic negative quadrupole moment of CO₂ and sought to use electrostatic complementarity as a new principle for selective separation,” says Prof. Hori. “The layered crystal unexpectedly showed that its interlayer space could expand in response to guest molecules.”

In its guest-free state, the crystal contains ultramicropores measuring about 2.6 Å across. These spaces are too small to serve as conventional pathways for CO₂, yet they act as triggers. Fluorinated aromatic surfaces create positively polarized regions that favor molecules with complementary electrostatic distributions. When a suitable guest approaches, the layers move apart, allowing larger molecules to enter.

This adaptive behavior was especially striking for CO₂. At 195 K, appreciable CO₂ uptake was observed at pressures as low as 2.0 Pa, reaching about 0.2 molecules per [Zn(L)Py]₂ unit at 26 Pa and about 2.0 molecules per unit at 98 kPa. Even at 298 K, the uptake remained substantial at 0.58 mol mol⁻¹ near 98 kPa. CO₂ inclusion caused reversible expansion along the a-axis, showing that adsorption involved structural adaptation rather than filling the original ultramicropores.

The material also distinguished CO₂ from nitrogen and methane. At 303 K, CO₂ was retained longer than both gases. Under dry conditions, its breakthrough delay was about 60 seconds relative to nitrogen and 52 seconds relative to methane. This selectivity remained under highly humid conditions, with CO₂ uptake of 0.25 mol mol⁻¹ for CO₂/N₂ and 0.21 mol mol⁻¹ for CO₂/CH₄. These findings point to usefulness for gas purification.

The crystal could also recognize larger organic molecules. Although benzene is about 5.9 Å across, more than twice the intrinsic pore diameter, it entered the expanded crystal. When exposed to an equimolar benzene–hexafluorobenzene mixture, the crystal almost quantitatively incorporated benzene, reaching about 97% of its benzene-inclusion capacity, while no evidence of hexafluorobenzene insertion was observed. Benzene was also strongly favored over cyclohexane and cyclohexene in competitive experiments, demonstrating recognition based on electrostatic complementarity rather than molecular size alone.

“Chemical separations often depend on rigid pores or energy-intensive processes, but our crystal responds directly to favorable interactions with selected molecules,” says Prof. Hori. “This adaptive mechanism could provide a route toward more energy-efficient CO₂ capture and the separation of closely related organic compounds that are difficult to distinguish by conventional methods.”

Overall, the study establishes interlayer adaptive crystals as a new approach to molecular recognition, combining porous-material uptake with molecular-crystal precision. Fluorinated surfaces guide guest recognition and trigger reversible layer expansion, enabling CO₂ uptake at very low pressure, selective separation from nitrogen and methane under highly humid conditions, and selective benzene recognition. The concept could support CO₂ purification, organic-compound separation, controlled molecular transport, confined reactions, and guest-responsive materials.