Preparation of Copper Nanoparticles in Chitosan Membranes and their Application as Irreversible Humidity Indicators

Copper nanoparticles were prepared in chitosan (CHI) membranes via reduction of CuSO4.5H2O with sodium borohydride (BH). The fabrication process was performed in two steps: (1) first adsorbing Cu(II) ions in the CHI membranes, followed by (2) a chemical reduction of the Cu(II) ions to zero-valent copper (using BH). This study used SEM, DSC, and XRD to examine the morphological, thermal and chemical properties of the CHI-copper membranes. The synthesized CHI-copper membranes were exposed to ambient humidity and characterized by digital-image analysis with RGB color standards. The results showed that the CHI-copper membranes produced were successfully able to detect ambient moisture shown by the color changes of the membranes (from dark brown to blue). These CHI-copper membranes hold great promise in the engineering field for the production of humidity indicators and sensors.