A tetraphenylethylene-based superphane for selective detection and adsorption of trace picric acid in aqueous media

Picric acid is known as one of the most dangerous explosive materials and it has become one of the main pollutants in soil and, inter alia, groundwater. To date, many organic or inorganic probes have been reported to detect picric acid, especially in organic solvent systems. Nonetheless, the detection and adsorption of trace (sub-ppm or ppb level) picric acid in aqueous media remain challenging. Herein, we describe the facile synthesis of a tetraphenylethylene-based superphane cage via [6 + 2] condensation of dialdehyde and hexakis-amine, followed by a NaBH4-mediated reduction. This purely covalent organic cage was found able to show aggregation enhanced emission in a mixture of tetrahydrofuran and water (1:9, v/v), which can be utilised as a probe for detection of picric acid with ultrahigh sensitivity (as low as 0.9 ppb) and selectivity (against other tested nitroaromatic compounds). More importantly, this new superphane cage can serve as a new nonporous amorphous superadsorbent (NAS) material for adsorption of picric acid with an exceptional maximum uptake capability of 454 mg g(-1). It also proved able to eliminate trace picric acid from aqueous media with up to 99% removal efficiency, meeting the discharge standard (<1.0 ppb). As such, we believe that this study offers new insight into the design and synthesis of NAS-based advanced materials for sensitive and selective detection and adsorption of trace pollutants from complex aqueous wastes. [GRAPHICS] .