Urethane-Linked Imidazole-Cellulose Microcrystals: Synthesis and Their Dual Functions in Adsorption and Naked Eye Sensing with Colorimetric Enhancement of Metal Ions

In this work, we demonstrate a simple approach to synthesize urethane-linked imidazole-cellulose microcrystals (U-ICMs) for simultaneous adsorption and naked eye sensing of metal ions. The synthesis is based on surface chemical modification of cellulose microcrystals (CMCs) by 1,1-carbonyldiimidazole and 1-(3-aminopropyl)imidazole, respectively. The adsorption and sensing of U-ICMs and CMCs in response to diverse metal ions (Fe 2+, Fe 3+, Co 2+, Ni 2+, Cu 2+, Zn 2+, Ag +, and Cd 2+ ) are qualitatively and quantitatively elucidated by UV–vis spectroscopy, inductively coupled plasma-optical emission spectroscopy, and X-ray photoelectron spectroscopy (XPS). The U-ICMs exhibit high performance for most metal species adsorption including Fe 2+, Co 2+, Ni 2+, Cu 2+, Zn 2+, Ag +, and Cd 2+, while CMCs favor Fe 3+ adsorption. Comparing the adsorption performance of CMCs and U-ICMs, the presence of urethane-linked imidazole on CMCs leads to an improvement of adsorption capacity of more than 3 times (for Zn 2+ ) up to 23 times (for Ni 2+ ). At the same time, the adsorption of metals on U-ICMs promotes an enrichment of metal colors that can be clearly observed by the naked eye and UV–vis spectroscopic data. XPS and X-ray absorption near-edge structure are investigated to prove how those metal ions transform after exposure to the unmodified and modified CMCs surface. The findings highlight the potential use of U-ICMs together with CMCs as sustainable bioadsorbents and sensing materials for metal separation and water purification.