Synthesis of gelatin-based nano copper and investigation of its humidity sensing properties by QCM system

During the synthesis of nanoparticles, various coating agents are used to keep the nanoparticles stable. This study aimed to determine the most effective sensor by examining the sensing properties of quartz crystal microbalance (QCM) sensors coated with gelatin-based copper nanoparticles synthesized by reduction method against different humidity environments. For this purpose, gelatin-based CuNPs were synthesized using different synthesis parameters to be coated on the QCM crystal surface, and their structures were elucidated by UV-Vis spectrophotometer, STEM analysis, and contact angle measurements. In order to investigate the effect of the synthesis parameters used in obtaining CuNPs on humidity sensing properties, QCM crystals coated with CuNPs obtained by changing the parameters such as CuSO4.5H2O as copper source, gelatin as coating agent and NaBH4 as reducing agent were exposed to 11% (lowest) and 98% (highest) relative humidity environments. The optimum synthesis parameters were determined for CuNP, from which the sensor with the highest frequency response was obtained. In addition, the QCM-7 sensor, where the highest response was observed, was exposed to different humidity environments such as 11%, 32%, 44%, 54%, 64%, 75%, 84% and 98%, and the relationship between the sensor response and the relative humidity increase was observed. Repeatability tests of the QCM-7 sensor against a 98% relative humidity environment with 4 consecutive repeat experiments and stability tests, once a day for 15 days, were also performed. Finally, sensors with different coating thicknesses (800 Hz, 1760 Hz, 3940 Hz, and 12700 Hz) were created using the synthesis parameters determined for CuNPs, where the best sensor responses were observed. The obtained sensors were exposed to 11% and 98% relative humidity environments, and it was determined that the increase in the coating amount caused an increase in the frequency response of the sensor against the relative humidity environment.