Rhodamine Derivative- Based Cellulose Acetate Electrospun Colorimetric Sensor for Cu2+ Sensing in Water: Effects of Alkaline Treatment

This is the first investigation of a rhodamine B derivative (RBD)/cellulose acetate (CA) colorimetric test strip for Cu2+ sensing in water. The test strip allowed both semi-quantitative naked-eye detection and quantitative detection when spectroscopy was applied. A chemosensor, RBD, was doped into a CA solution and this was electrospun to produce a test strip. The average diameter of the electrospun fibers was 750 +/- 270 nm. The nonwoven test strip changed from off-white to pink when exposed to aqueous Cu2+ solutions. A linear relationship was found between the color strength of the test strip and the Cu2+ concentration (20-300 ppm, R-2=0.989). The limit of detection (LOD) was 18 ppm. Alkaline treatment of the electrospun sample with sodium hydroxide produced partial deacetylation of the CA, reducing the number of acetyl groups while increasing the number of hydroxyl groups in the fibrous structure. Fiber swelling and improved wettability of the solid sensor was also observed. The treated sensor responded approximately 33 times faster to Cu2+ than the untreated sensor. When tested with Cu2+, the sensor produced K/S values approximately 5-10 times greater than when tested with Mn2+, Pb2+, Cd2+, Ni2+, Zn2+ or Sn2+, and three times greater than Fe2+. The electrospun sensor showed a slight improvement in Cu2+ adsorption after alkaline treatment.