Elemental mapping through energy-dispersive (EDS) X-ray spectroscopy has been carried out for the composite with 35 wt% of Cs2SnBr6, as an illustrative example, and is reported in Figure , confirming the formation of a composite between the two semiconductors. Electron paramagnetic resonance (EPR) measurements have been carried out on g-C3N4 nanosheets to confirm the presence of nitrogen vacancies which are characterized by the presence of a peculiar signal centered around g=2, as shown in Figure , due to the presence of unpaired electrons. 28 Experimental details are provided in the SI for both the photocatalytic experiments and the ammonia determination technique which is not based on colorimetric methods (which tend to overestimate the actual concentrations) but on a more accurate and interferent-free approach.