OICC Press Iranian Journal of Catalysis 2345-4865 15 3 2025 09 30 Thermal decomposition synthesis of novel quaternary heterojunction CuS/Cu9S5/Cu2O/C3N4 composites for enhanced visible-light-driven photocatalytic activity 10.57647/j.ijc.2025.1503.28 EN Prakasit Intaphong Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand; Multidisciplinary and Interdisciplinary School, Chiang Mai University, Chiang Mai, 50200, Thailand Pasu Inphak Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand; Multidisciplinary and Interdisciplinary School, Chiang Mai University, Chiang Mai, 50200, Thailand Sujitra Tandorn Office of Research Administration, Chiang Mai University, Chiang Mai, 50200 Thailand Komsanti Chokethawai Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand Chamnan Randorn Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand; Centre of Excellence in Materials Science and Technology, Chiang Mai University, Chiang Mai, 50200, Thailand Journal Article 2025 09 30 The novel quaternary heterojunction copper sulfide/cuprous sulfide/cuprous oxide/carbon nitride (CuS/Cu9S5/Cu2O/C3N4) composite was prepared by thermal decomposition. The phase, composition, morphologies, and oxidation state of elements in as-prepared heterojunction multiphase Cu-based composites were characterized and discussed in this research. The XRD, SEM, and TEM analyses showed the binary CuS/Cu9S5 composite at 400-450 oC and quaternary heterojunction CuS/Cu9S5/Cu2O/C3N4 composite at 500-600 oC, which presented the mixed irregular sheets and agglomerated particles in shape. The photocatalytic activities of heterojunction multiphase Cu-based composites were studied by methyl orange (MO) degradation under visible light irradiation. It was found that the CuS/Cu9S5/Cu2O/C3N4 composite at 600 °C showed the highest photodegradation efficiencies of MO at 90.06% under visible light irradiation within 150 min due to the charge diffusion at the CuS/Cu9S5/Cu2O/C3N4 interface. The active species for MO degradation over CuS/Cu9S5/Cu2O/C3N4 composite were analyzed by scavenger test, which reveals that the ●O2- radicals and h+ are the main and minor active species for MO degradation photocatalyzed by the CuS/Cu9S5/Cu2O/C3N4 composite under visible light irradiation.  Finally, the photodegradation efficiency of MO in the presence of the CuS/Cu9S5/Cu2O/C3N4 composite at 600°C decreased by  85.89% after five cycles, demonstrating its high stability and reusability for practical photocatalytic applications.