Heterojunction photocatalyst MnO2-CsSnI3 for highly efficient formaldehyde oxidation at room temperature

•A Z-scheme heterojunction catalyst MnO2-CsSnI3 was successfully synthesized.•Record high degradation efficiency has reached over 85 % at initial 15 min, while the final degradation efficiency up to 99.6 % (0.03 ppm) after 3 h operation.•The generation of large amount •O2− and •OH radicals is the key source for the excellent HCHO degradation performance. The effective removal of the low-concentration formaldehyde (HCHO) in the indoor environment is a critical issue affecting the quality of people’s daily lives. In this study, heterojunction catalysts composed of manganese dioxide (MnO2) and cesium tin iodine (CsSnI3) nanocrystals were first synthesized and successfully used for photocatalytic HCHO degradation. After the full band light irradiation (150 mW/cm2) for 3 h, the concentration of HCHO decreased from 7 ppm to a minimum of 0.03 ppm at room temperature (25 °C, 25 % RH, degradation efficiency reaches up to 99.6 %). Subsequent analysis using electron paramagnetic resonance (EPR) and transmission electron microscopy (TEM) revealed that the MnO2-CsSnI3 heterojunction photocatalyst not only offers a Z-scheme charge-transfer pathway but also promotes the generation of a large number of •O2− and •OH. Compared to the single-phase material, the concentration of •O2− and •OH has increased by 1.5 times. This MnO2-based Z-scheme heterojunction photocatalyst provides a novel strategy for the degradation of low-concentration HCHO in practical indoor environments.