Roberto C. DanteJirawat TrakulmututaSiwaporn Meejoo-SmithPablo Martín-RamosPedro Chamorro-PosadaDario RuttoFrancisco M. Sánchez-ArévaloUniversidad Nacional Autónoma de MéxicoUniversidad de ValladolidUniversidad de ZaragozaMahidol UniversityBurgo GroupResearch2020-01-272020-01-272019-06-01Materials Chemistry and Physics. Vol.231, (2019), 351-356025405842-s2.0-85064805363https://repository.li.mahidol.ac.th/handle/20.500.14594/51175© 2019 Elsevier B.V. Methylene blue (MB)is a dye widely used as an optical redox indicator in analytical chemistry, whose color change is also affected by pH. It was irreversibly adsorbed on polymeric carbon nitride (g-C3N4)prepared either from urea or from melamine cyanurate. Electron spin resonance (ESR)showed an increase in radicals or unpaired electrons in the MB-g-C3N4 system in comparison to pure g-C3N4. Upon treatment with potassium hydroxide, an abrupt color change from blue to purple occurred, together with a decrease in the ESR signal. Exposure to air caused a shift to the initial blue color, and, as suggested by UV-Vis spectroscopy data, the system returned to its original state, before the treatment with alkali. This behavior suggests the suitability of the MB-g-C3N4 system as a promising reusable sensor for the detection of exposure to air (and/or to carbon dioxide)of products stored under vacuum or in a controlled atmosphere. Thus, visual indicators based on this material may find applications as cost-effective leakage indicators for the modified atmosphere package (MAPs)industry, in particular to assess food safety or for electronic packaging.Mahidol UniversityMaterials ScienceArticleSCOPUS10.1016/j.matchemphys.2019.04.031