Using differential thermal analysis and thermogravimetry, we have studied thermal decomposition of a mechanical mixture of thiourea and zinc acetate, resulting in the formation of a composite material consisting of graphitic carbon nitride and zinc acetate, g-C3N4/ZnS, and possibly containing zinc oxide (ZnO) inclusions. In the case of a mixture containing the stoichiometric sulfur:zinc ratio for zinc sulfide synthesis, one can obtain a material containing only ZnS semiconductor crystals embedded in a g-C3N4 matrix. ZnS is formed in the temperature range 317–367 °C as a result of decomposition of zinc complexes with thiourea. Heating the mixture to above 560 °C increases the rate of the thermal decomposition of g-C3N4, which reaches completion between 720 and 740 °C. The presence of oxygen in the reaction atmosphere also accelerates this process, without significantly changing the temperature range of synthesis or decomposition of reaction products. The proposed technique can be used for the synthesis of g-C3N4-based composite materials and other semiconducting metal sulfides
