Highly Selective and Rapid Naked-Eye Colorimetric Sensing and Fluorescent Studies of Cu²⁺ Ions Derived from Spherical Nanocellulose

Nanocellulose has emerged as the most promising sustainable nanomaterial to develop cost-effective smart materials for various applications with consequential positive environmental impact. In the present study, we report spherical nanocellulose (SNC) modified with diethylenetriamine (DETA) and/or ethanolamine (EA) (SNC-DETA, SNC-EA, and SNC-DETA-EA) as Cu2+ ion sensors. Structure dependence of the sensing properties is the highlight of this work, as SNC-DETA-EA and SNC-DETA showed colorimetric naked-eye and fluorescent activity, with the former showing the same at very low ion concentrations with high selectivity, whereas SNC-EA lacked the same. The solution color changed rapidly to deep blue, and the fluorescence intensity was quenched when the ion concentration increased in the range 0.5–100 ppm, thus facilitating dual-channel ion detection. SNC-DETA-EA showed 1.03 ppm or a 1.622 × 10–5 M limit of detection and high Cu2+ ion uptake with maximum Langmuir capacity (qm) of 212.76 mg/g.