Truly reversible capture of hydrogen was achieved at ambient conditions on Pd-loaded organo-montmorillonites obtained by photo-addition of different thiols on propargylated-TRIS cations already grafted on the clay surface. TEM insights showed that more than 90% of Pd incorporated occur as 0.3-0.5 nm subnanoparticles (PdSNPs). XPS and NMR analyses revealed simultaneous strong S:Pd and O:Pd-0 interactions that "cement" the organic moiety around PdSNPs. The significant decrease in porosity suggests a compacted structure that impedes not only metal aggregation, but also hydrogen diffusion in the metal bulk. Thus, hydrogen appears to adsorb mainly via physical condensation around PdSNPs. These thiol-clay matrices showed hydrogen surface affinity factors of up to 0.51 mmol m(-2) at ambient temperature and pressure. This is higher than those reported for much more sophisticated materials. DSC measurements showed very low desorption heat between 20 and 80 degrees C. Hydrogen release was achieved merely under vacuum or slight heating starting from 40 degrees C and was almost completed up to 85 degrees C. This provides a proof of concept of truly reversible capture of hydrogen for concentration and/or storage purposes. Such a performance has never been achieved at ambient temperature and pressure. These findings open new prospects to develop low-cost materials for reversible hydrogen storage without energy and safety constraints. (C) 2016 Elsevier B.V. All rights reserved.