An electrodeless quartz crystal resonator integrated with UV/Vis spectroscopy for the investigation of the photodecomposition of methylene blue

The photodecomposition of organic molecules (methylene blue) was investigated using an integrated system consisting of a UV–vis spectrometer and an electrodeless quartz crystal microbalance (EL-QCM). ZnO nanorods were directly grown on a bare quartz crystal and methylene blue was coated onto the nanorods by drop-casting. Ring-type remote electrodes were used to enable the transmission of light. As the coated methylene blue was photo decomposed by UV light, the changes in mass and light transmittance were measured with the EL-QCM and UV–vis spectrometer respectively. These simultaneous measurements revealed that the rate of change in optical transmission is greater than that of the mass in the early stage of photodecomposition, which indicates that the structural degradation of methylene blue is dominant in the early stage. In contrast, the changes in light transmittance were linearly proportional to those in mass during the later stages, which is attributed to the mineralization of methylene blue.