Cationic Waste Cotton Fabric for the Adsorptive Colorimetric Detection of Chromium Ion Traces

Hexavalent chromium (Cr­(VI)) exists in water as carcinogenic anionic species. Here, waste cotton fabric (WCF) was recycled and given a second life as a support for Cr­(VI) colorimetric detection. WCF was prepared by grafting 2,3-epoxypropyltrimethylammonium chloride on its surface to make it cationic (cWCF) and suitable for Cr anion adsorption via electrostatic interactions. Two strategies were assessed for Cr­(VI) detection in water. In the first method, cWCF was functionalized with color-developing 1,5-diphenylcarbazide (DPC), and the resulting strip was evaluated for Cr­(VI) quantification. This sensor exhibited a short response time of 30 s with a limit of detection (LOD) of 0.029 mg/L. In the second method, Cr­(VI)-containing samples were initially preconcentrated by adsorption on the cWCF substrate, and then, DPC was added for color development. With this system, the LOD was excellent at 0.0013 mg/L, but the response time was longer at 5 min. Another advantage of the robust cWCF support is that it could be washed and reused multiple times for Cr­(VI) detection. The two approaches described here are inexpensive and can be selected for different purposes depending on the sensitivity required as well as the volume of samples and time available to complete the Cr ion assay.