Composites of titanium-based metal–organic frameworks (MOF) and various carbon nitride polymers with stoichiometry close to C3N4 exemplified by heptazine-based melon, poly(triazine imide) and poly(heptazine imide), will be designed for obtaining efficient, potentially noble metal-free photocatalysts for hydrogen production upon visible-light irradiation. The structure of these composites will be optimized by fitting the positions of the conduction and valence bands of the components in order to achieve efficient charge separation within the photocatalytic systems that is expected to increase the reaction rates. Moreover, we intend to gain information about the interaction mechanism of the composites phases by electronic paramagnetic resonance studies.