Arsenate Anion-π Interactions on Amine-Modified Polydivinylbenzene in Aqueous Systems: Experimental and Theoretical Investigation.

Anion-π interactions aiding in the adsorption of anions in the solution phase, though challenging to quantify, have attracted a lot of attention in supramolecular chemistry. We present the design of a polymer adsorbent that quantifies the adsorption of arsenate ions experimentally by optimizing anion-π interactions in a purely aqueous system and use density functional theory to compare these results with theoretical data. Arsenate anions are removed from water by amine-functionalized polydivinylbenzene using the comonomer 1-vinyl-1,2,4-triazole, which was cross-linked with divinylbenzene via radical polymerization in a hydrothermal procedure. The amine-functionalized polydivinylbenzene successfully removed arsenate anions from water with a capacity of 46 mg g-1, a 70% increase compared to the nonfunctionalized polydivinylbenzene (27 mg g-1) capacity under the same conditions. Adsorption is best described by the Sips isotherm model with a correlation coefficient R2 factor of 0.99, indicating that adsorption sites are homogeneous, and adsorption occurred by forming a monolayer. Kinetic studies indicated that adsorption is second order in the amine-functionalized polydivinylbenzene. Computational studies using density functional theory showed that the 1-vinyl-1,2,4-triazole comonomer improved the thermodynamic stability of the anionic-π interactions of polydivinylbenzene with arsenate anions. Electrostatic interactions dominate the mechanism of adsorption in polydivinylbenzene compared to the anion-induced interactions that dominate adsorption in amine-functionalized polydivinylbenzene.

Modified Mesoporous Silica for Efficient Siloxane Capture.

In this study, octamethylcyclotetrasiloxane (D4) was removed by using a novel modified solid adsorbent of mesoporous silica. The adsorbent was synthesized using inverse micelles with some modifications in the synthesis process (temperature of gelation) and in the post treatment conditions (calcination temperature and heating rate) with a concomitant improvement of D4 uptake. This is the first report on regulating the textural properties of the mesoporous silica material UCT-14 to develop an active silica adsorbent. These adjustments resulted in an increase of the silica surface area from 391 to 798 m(2)·g(-1), which leads to a high capacity (686 mg·g(-1)) of D4-capture for the silica synthesized at 80 °C, calcined at 450 °C with the heating rate of 100 °C·min(-1) (Si-Syn80). This adsorbent showed comparable adsorption performance with the widely used commercial silica gel under dry and humid condition. Recyclability tests on the commercial silica gel and mesoporous silica synthesized at 120 °C and calcined at 450 °C with a heating rate of 100 °C·min(-1) (called Si-Syn120 or Si-450 or Si-100 °C·min(-1)) indicated that the Si-Syn120 (capacity drop 10%) is more efficient than silica gel (capacity drop 15%) after three cycles. Although, the presence of moisture (25%) in the nitrogen gas stream led to capacity reduction in both Si-Syn120 and commercial silica gel, the modified UCT-14 shows slightly better resistance to humid condition.