Abstract: An example article includes a substrate and a coating applied to the substrate. The coating includes a stabilizer and an organic phosphonic acid reactant. In an example article, the coating includes a water-soluble polymer and an organic phosphate or phosphonate reactant. An example coating configured to be applied to a basic gas filter substrate includes a water-soluble polymer and an organic phosphate or phosphonate reactant. An example technique includes applying a coating to a substrate and heating at least the coating to a temperature between about 100° C. and about 275° C. for about 1 minute to about 10 minutes. An example system includes a basic gas filter including a coating, and a sensor configured to sense an optical change in the coating.

Abstract: An example article includes a substrate and a coating applied to the substrate. The coating may include a basic reactant and a humectant. The coating may further include a preservative or a water-soluble polymer. A coating configured to be applied to an acidic gas filter substrate may include K2CO3, potassium succinate, dehydroacetic acid, and poly(2-acrylamido-2-methyl-1-propanesulfonic acid (PAMPS). An example system includes an acidic gas filter including a coating, and a sensor configured to sense an optical change in the coating.