Photo-decontamination catalyst material

Periodic mesoporous organosilica (PMOs) combined with a porphyrin achieves a semi-selective sensing element for the optical detection of cyclic organics and a material to catalyze the conversion of nitroaromatics under sunlight

Materials Environmental

Periodic mesoporous organosilicas (PMOs) are organic-inorganic polymers with highly ordered pore networks and large internal surface areas. Due to their structural stability, functionality, and specificity, PMOs are very efficient sorbents for the removal, sequestration, and pre-concentration of pollutants and any targeted compound from both vapor and liquid phase.

U.S. Navy Sailors remove clothing from a simulated victim during decontamination operations training. (Aaron Henson/Marine Corps)

The use of functionalized PMO for the preferential adsorption of hydrocarbons over time scales on the order of minutes is common. Other applications of PMOs include catalysis, filtration, purification, and chemical sensing. Decontamination applications involving PMO materials are based on adsorption of the contaminant onto the silicate, and not on the degradation of the contaminant. Yet a secondary means, such as a spectroscopic or electrochemical technique, is required for the specific detection of the sorbate.

A porphyrin is a nearly flat molecule of twenty carbon and four nitrogen atoms consisting of four pyrrole rings joined by methine bridges. They have been used as catalysts in a wide range of applications: degradation of chlorinated phenols, nitro-substituted toluene, and atrazine; oxidation of alkylaromatics; and oxidative cleavage of C—C bonds. When compared to proteins and microorganisms, porphyrins and metalloporphyrins are much less sensitive to variations in conditions such as temperature and pH than proteins and microorganisms and have been shown to withstand temperatures above 150° C.

Navy researchers have combined PMO material with the optically active porphyrin molecule as a catalyst in photo-decontamination applications, as well as a detection element for a stand-off point detection system. The material provides a degree of selectivity allowing for binding of compounds within a class, for example, aromatics. The material catalyzes the degradation of the contaminant using sunlight, allowing for reuse of the PMO material for repeated detection and decontamination applications. The PMOs can be optimized for adsorption of TNT and similar compounds, however, PMO materials can be synthesized for adsorption of many materials, including, chemical warfare agents, pesticides, volatile organic compounds, or toxic industrial products. Potential applications include situations such as inline water treatment, environmental cleanup, and exhaust stack filtering.

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