A novel hybrid material (gC(3)N(4)-rFe) consisting of amine-rich graphitic carbon nitride (gC(3)N(4)), decorated with reduced iron nanoparticles (rFe) is presented. XRD and TEM show that gC3N4-rFe bears aggregation-free Fe-nanoparticles (10 nm) uniformly dispersed over the gC3N4 surface. In contrast, non supported iron nanoparticles are strongly aggregated, with non -uniform size distribution (20-100 nm). 57Fe-Mossbauer spectroscopy, dual -mode electron paramagnetic resonance (EPR) and magnetization measurements, allow a detailed mapping of the evolution of the Fe-phases after exposure to ambient O-2. The as-prepared gC(3)N(4)-rFe bears Fe2+ and Fe phases, however only after long exposure to ambient O-2, a Fe -oxide layer is formed around the Fe core. In this [Fe/Fe-oxide] core-shell configuration, the gC(3)N(4)rFe hybrid shows enhanced As" uptake capacity of 76.5 mg g(-1), i.e., ca 90% higher than the unmodified carbonaceous support, and 300% higher than the non -supported Fe-nanoparticles. gC(3)N(4)-rFe is a superior As" sorbent i.e., compared to its single counterparts or vs. graphite/graphite oxide or activated carbon analogues (11-36 mg g(-1)). The present results demonstrate that the gC(3)N(4) matrix is not simply a net that holds the particles, but rather an active component that determines particle formation dynamics and ultimately their redox profile, size and surface dispersion homogeneity. (C) 2016 Elsevier B.V. All rights reserved.