High-performance TNT chemosensory materials based on nanocomposites with bimodal porous structures

A series of porphyrin or metalloporphyrin-doped silica films with bimodal porous structures were successfully fabricated using polystyrene spheres and a surfactant (CTAB) as structure-directing agents, and examined for chemosensory applications to detect trace amounts of vapours of explosives such as TNT (2,4,6-trinitrotoluene), DNT (2,4-dinitrotoluene) and NB (nitrobenzene). The obtained results clearly show that an appropriate combination of macropores and mesopores can achieve high molecule permeability and high density of interaction sites (sensing elements-analyte). As a result, silica films with bimodal porous structures exhibit much more efficient fluorescence response capability than single modal porous films. Films with extremely high fluorescence quenching efficiency towards TNT (10 ppb), close to 55% after 10 s of exposure, were achieved, which is nearly double those of conjugated-polymer based TNT sensor materials. Using toluene washing, the sensory properties of the constructed films can be easily recovered. Besides the remarkable TNT detecting capability, these hybrid films have several advantages over other fluorescence-based sensory materials, such as a simple preparation approach, inexpensive materials, recognition ability of different nitroaromatics as well as stability of organic sensing elements in inorganic matrices. These results suggest that this new kind of mesostructured nanocomposite is a potentially useful chemosensory material for rapidly detecting trace explosives.