Onsite paper-type colorimetric detector with enhanced sensitivity for alkali ion via polydiacetylene-nanoporous rice husk silica composites.

A paper-type colorimetric detector for identifying the degree of alkali ion concentration with the naked eye was fabricated using polydiacetylene/nanoporous rice husk silica (PDA/NP-SiO) nanocomposites as a potentially effective, rapid, and facile approach to detect alkali ion in aqueous solution. This study is worth investigating because it has the advantage of visually confirming the alkaline ion in aqueous solution without the aid of other analytical instruments directly at on-site as if pH indicator analysis. The concept of this study is the facile synthetic route of PDA and NP-SiO. Nanoporous rice husk silica (NP-SiO) with a high specific surface area 450 m/g was extracted from leached rice husk ash via a sol-gel process and utilized for efficient absorption of alkali ion. PDA was used as a material to differentiate the degree of alkali ion drawing using only the change of color. By compositing these two materials on the surface of filter paper using the spray drying method, the resulting PDA/NP-SiO composites with NP-SiO of the different specific surface areas showed a different change of color indicated by the degree of alkali ions even at a low concentration of less than 122 μm. The composite was further analyzed by UV spectroscopy for a change of color and images for screening depending on the alkali ion concentrations. The color response percentage of the PDA/NP-SiO composites (PDA/449S; S 449.9213 m/g) was 23.39% at 0.122 mM of NHOH. Consequently, the result from this study showed the possibility of sensitively distinguishing the alkali ions ranging from pH 9.86 to pH 11.38 using only the naked eye, brought potential features that can be used as a convenient and facile primary water testing kit in practical applications.