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.

Adsorptive Biogas Purification from Siloxanes—A Critical Review

Siloxanes are among the most technologically troublesome trace compounds present in biogas. As a result of their combustion, hard-to-remove sediments are formed, blocking biogas energy processing devices and reducing the efficiency of biogas plants. The purpose of this study was to help investors and designers to choose the optimal technology for the adsorptive removal of volatile methylsiloxanes (VMSs) from biogas and to identify adsorbents worth further development. This paper critically reviews and discusses the state-of-the-art technologies for the adsorption removal of siloxanes from biogas, indicating potentially beneficial directions in their development and deficiencies in the state of knowledge. The origin of VMSs in biogas, their selected physicochemical properties, technological problems that they can cause and their typical versus limit concentrations in biogases are presented. Both the already implemented methods of adsorptive VMSs removal from landfill and sewage gases and the ones being under development are verified and systematized. The parameters and effectiveness of adsorption processes are discussed, and individual adsorbents are compared. Possible ways of regenerating spent adsorbents are evaluated and prospects for their application are assessed. Finally, zeolite-based adsorbents—which can also be used for biogas desulfurization—and adsorbents based on polymer resins, as being particularly active against VMSs and most amenable to multiple regeneration, are identified.

Facile and Green Synthesis of Saturated Cyclic Amines

Single-nitrogen containing saturated cyclic amines are an important part of both natural and synthetic bioactive compounds. A number of methodologies have been developed for the synthesis of aziridines, azetidines, pyrrolidines, piperidines, azepanes and azocanes. This review highlights some facile and green synthetic routes for the synthesis of unsubstituted, multisubstituted and highly functionalized saturated cyclic amines including one-pot, microwave assisted, metal-free, solvent-free and in aqueous media.