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.