Colorimetric detection of gaseous ammonia by polyaniline nanocoating of natural cellulose substances

A sensitive and reversible colorimetric gaseous ammonia sensor was prepared by covering each nanofiber of natural cellulose substance (e.g., common commercial filter paper) with ultrathin polyaniline films via in situ polymerization of aniline molecules. The thickness of the deposited emeraldine salt state polyaniline film was ∼10 nm. The natural hierarchical network of the initial filter paper was preserved at nanoprecision, and obvious color change of polyaniline from green to blue was achieved within 5 min at 30 °C in the presence of gaseous or aqueous ammonia. The respective detection limits by the naked eyes were 100 ppm for gaseous ammonia in nitrogen and 10 ppm for evaporated ammonia aqueous solution. Moreover, the obtained colorimetric sensing sheet endured reversible gaseous ammonia detection for at least 50 times. The current ultrathin polyaniline surface coating approach with natural cellulose substances as scaffolds opens a low-cost, facile, and effective route to improve sensitivity of colorimetric gaseous ammonia detectors.