Surface-Tension-Governed Nanoconfinement for Tunable Hydrogen-Isotope Transport

Interfacial forces and nanoconfined environments play crucial roles in transport phenomena within low-dimensional materials. In this study, we propose a photothermally regulated surface-tension mechanism for hydrogen-isotope fractionation, in which light-induced changes in the surface tension of gallium ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>Ga</a:mi> </a:math> ) dynamically modulate the confined environment between graphene oxide ( <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi>GO</c:mi> </c:math> ) layers. Under near-infrared irradiation, the surface tension of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mi>Ga</e:mi> </e:math> decreases, altering its wettability within the interlayer galleries and inducing a reversible contraction of the <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi>GO</g:mi> </g:math> interlayer spacing. temperature-dependent transmission electron microscopy confirmed this dynamic modulation, showing that confined <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mi>Ga</i:mi> </i:math> nanoparticles undergo fully reversible expansion-contraction and display surface-energy-driven extension behavior analogous to macroscopic particles. Such confinement-induced structural responsiveness regulates the local arrangement of water molecules, leading to distinct molecular aggregation states for <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:msub> <k:mrow> <k:mrow> <k:mi mathvariant="normal">H</k:mi> </k:mrow> </k:mrow> <k:mn>2</k:mn> </k:msub> <k:mrow> <k:mrow> <k:mi mathvariant="normal">O</k:mi> </k:mrow> </k:mrow> </k:math> and <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"> <o:msub> <o:mrow> <o:mrow> <o:mi mathvariant="normal">D</o:mi> </o:mrow> </o:mrow> <o:mn>2</o:mn> </o:msub> <o:mrow> <o:mrow> <o:mi mathvariant="normal">O</o:mi> </o:mrow> </o:mrow> </o:math> . Due to stronger intermolecular attraction, <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:msub> <s:mrow> <s:mrow> <s:mi mathvariant="normal">D</s:mi> </s:mrow> </s:mrow> <s:mn>2</s:mn> </s:msub> <s:mrow> <s:mrow> <s:mi mathvariant="normal">O</s:mi> </s:mrow> </s:mrow> </s:math> diffusion is more restricted in confinement, leading to pronounced isotope selectivity. Experimentally, the membrane achieved a separation factor of 70.53 for <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"> <w:msub> <w:mrow> <w:mrow> <w:mi mathvariant="normal">H</w:mi> </w:mrow> </w:mrow> <w:mn>2</w:mn> </w:msub> <w:mrow> <w:mrow> <w:mi mathvariant="normal">O</w:mi> </w:mrow> </w:mrow> <w:mo>:</w:mo> <w:msub> <w:mrow> <w:mrow> <w:mi mathvariant="normal">D</w:mi> </w:mrow> </w:mrow> <w:mn>2</w:mn> </w:msub> <w:mrow> <w:mrow> <w:mi mathvariant="normal">O</w:mi> </w:mrow> </w:mrow> </w:math> and demonstrated selective removal of tritium water ( <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"> <cb:msub> <cb:mrow> <cb:mrow> <cb:mi mathvariant="normal">T</cb:mi> </cb:mrow> </cb:mrow> <cb:mn>2</cb:mn> </cb:msub> <cb:mrow> <cb:mrow> <cb:mi mathvariant="normal">O</cb:mi> </cb:mrow> </cb:mrow> </cb:math> ). Our study elucidates the interplay between photothermally driven interfacial energy modulation and confined molecular transport, offering new insights into tunable separation processes and interfacial physics.