Cobalt-impregnated cellulose composites: synthesis, characterization, and preliminary evaluation for humidity sensing

Colorimetric humidity sensing materials have significant applications in areas such as food preservation, packaging, and environmental monitoring. This study introduces a novel cobalt-impregnated cellulose–terephthalic acid (TPA) composite designed for qualitative colorimetric humidity sensing. The synthesis process involved the extraction of cellulose from sugarcane bagasse, followed by chemical cross-linking with TPA and in situ incorporation of cobalt ions. Additionally, a portion of the extracted cellulose was converted into microcrystalline cellulose (MCC) via acid hydrolysis to serve as a reference for structural characterization. Fourier Transform Infrared Spectroscopy (FTIR) and Powder X-ray Diffraction (PXRD) techniques were used to confirm their chemical composition and structural integrity. The resulting cobalt–cellulose–TPA composite exhibited distinct and reversible color changes in response to humidity, shifting from dark pink (hydrated) to purple (dehydrated), indicating its potential as a visual humidity sensor. This color change is attributed to reversible changes in the coordination geometry of Co 2+ ions, transitioning between octahedral and square planar configurations. Overall, the study demonstrates the feasibility of developing an eco-friendly, sustainable, and visually responsive humidity-sensing material from agricultural waste, with potential applications in cost-effective environmental and industrial monitoring systems.