Oxyanions like nitrates and phosphates are ubiquitous in nature and important to many of the planet’s natural functions, but studies have shown that regions of elevated oxyanion concentration are becoming increasingly prevalent. Excess concentrations of these anions can have negative ramifications on both environmental and human health. Excess phosphates in surface water systems are known to promote algal blooms that make water systems toxic or even fatal to small animals like fish and domestic pets, and nitrates in drinking water have been definitively linked to methemoglobinemia (blue baby syndrome). While many methods are being developed for nitrate and phosphate remediation, the Nell lab has focused on functionalized sorbents. In an effort to develop new ways of managing oxyanion concentrations in water systems, a small library of functionalized silica adsorbents have been synthesized using fumed silica, cab-o-sil® , by functionalizing the surface with 3-aminopropyltrimethoxysilane via a grafting method. Once the silica surfaces were functionalized with terminal amine groups, the surface was further functionalized with ligands that contained electron deficient aromatics. All of the ligands began as carboxylic acids, were converted into acid chlorides, and reacted with the amine functionalized materials. Some amines were left unfunctionalized to create a multifunctional surface, as an amine surface alone has been shown to bind anions from water. A variety of electron deficient carboxylic acids were purchased and used to create a set of materials with a range of electron withdrawing aromatics, included 4-sulfobenzoic acid potassium salt, 4-(trifluoromethyl)benzoic acid, 4-sulfobenzamide, and 3,5-dinitrobenzoic acid. Characterization of the sorbents was performed with powder X-ray diffraction spectroscopy, infrared spectroscopy, thermogravimetric analysis, and elemental analysis. Materials performance testing is ongoing for nitrate and phosphate.

Functionalized silica adsorbents for oxyanion trace capture

ACS Spring Meeting 2021

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