Abstract: The mercury detecting paper provides a visual indication of the presence of mercury in an applied water sample. The mercury detecting paper is formed as a hydrophobic substrate having a reagent layer deposited thereon. The hydrophobic substrate is made from paper having a layer of hexamethyldisilazane (HMDS) deposited thereon, and the reagent layer is a layer of 6-hydroxy-3-(2-oxoindolin-3-ylideneamino)-2-thioxo-2H-1,3-thiazin-4(3H)-one (HOTT). In use, a water sample is applied to the reagent layer and a visual color change of the reagent layer upon contact with the water sample indicates a presence of mercury in the water sample. Specifically, HOTT turns a brick red color upon contact with Hg2+ ions.

Abstract: The sunlight active composite photocatalyst for water purification includes ZnO (zinc oxide) and Co3O4 (cobalt II, III oxide). The composite photocatalyst may, in the presence of natural sunlight, achieve complete mineralization of chemical and biological contaminants in water without leaving any hazardous by-products. The composite photocatalyst may be synthesized by a sol gel route or process.