The purification of hydrogen prior of its use in various applications, such as fuel cells, is of paramount importance. Although there are many commercial ways to obtain hydrogen sulfide, the need to reach very low concentration values, at the ppm or even at the ppb level, is the main motivation behind this work. This work examines the production and utilization of a new, low H 2 S breakthrough and high capacity adsorbent, made of iron nanoparticles embedded in carbon nanofilaments. It is produced by a 2-step functionalization methodology: acid pretreatment and iron wet impregnation. This novel adsorbent was characterized by scanning transmission electron microscope, X-ray absorption near edge structure, Brunauer Emmet and Teller calculations, and thermogravimetric analysis, and the adsorption efficiency was measured for different iron-loadings, temperatures, and H 2 S breakthrough values. Operating conditions and metal-loading that allow a decrease of H 2 S concentration from 500 ppm to below 1.5 ppm are reported. It has also been found that acid treatment influences metal dispersion and, due to the nanometric nature of adsorbents, the process is not controlled by mass diffusion phenomena.