The study explores the tunable sieving of ions using graphene oxide (GO) membranes, which exhibit exceptional molecular permeation properties. However, their use in ion sieving and desalination is limited by a permeation cutoff of ~9 Å, larger than the hydrated diameters of common salts. The research focuses on controlling the interlayer spacing ($d$) of GO laminates to achieve smaller sieves, with the goal of achieving ion sieving smaller than typical ion hydrated diameters. By physically confining the GO laminates, the interlayer spacing can be reduced from ~9.8 Å to 6.4 Å, leading to accurate and tunable ion sieving. The ion permeation is found to be thermally activated with energy barriers of ~10–100 kJ/mol, depending on the interlayer spacing. Ion permeation rates decrease exponentially with decreasing sieve size, while water transport remains largely unaffected. This is attributed to the low barrier for water molecules and large slip lengths inside the graphene capillaries. The findings demonstrate a scalable method to obtain GO-based membranes with limited swelling, achieving 97% rejection for NaCl. The study also investigates the mechanism of ion permeation, suggesting that it is primarily driven by dehydration effects rather than pure size exclusion.The study explores the tunable sieving of ions using graphene oxide (GO) membranes, which exhibit exceptional molecular permeation properties. However, their use in ion sieving and desalination is limited by a permeation cutoff of ~9 Å, larger than the hydrated diameters of common salts. The research focuses on controlling the interlayer spacing ($d$) of GO laminates to achieve smaller sieves, with the goal of achieving ion sieving smaller than typical ion hydrated diameters. By physically confining the GO laminates, the interlayer spacing can be reduced from ~9.8 Å to 6.4 Å, leading to accurate and tunable ion sieving. The ion permeation is found to be thermally activated with energy barriers of ~10–100 kJ/mol, depending on the interlayer spacing. Ion permeation rates decrease exponentially with decreasing sieve size, while water transport remains largely unaffected. This is attributed to the low barrier for water molecules and large slip lengths inside the graphene capillaries. The findings demonstrate a scalable method to obtain GO-based membranes with limited swelling, achieving 97% rejection for NaCl. The study also investigates the mechanism of ion permeation, suggesting that it is primarily driven by dehydration effects rather than pure size exclusion.