Guanidinium-Based Ionic Covalent-Organic Nanosheets for Sequestration of Cr(VI) and As(V) Oxoanions in Water

Abstract

Chromium- and arsenic-based oxoanions are among the major highly toxic and carcinogenic inorganic pollutants present in groundwater, demanding fast and selective sequestration. Efficient capturing and removal of these highly mobile oxometallates at neutral pH presents a great challenge in groundwater cleanup. Herein, a series of guanidinium-based ionic organic covalent nanosheets (iCONs) with varying hydrogen bonding, steric, and electronic properties was studied to examine the structure–activity relationship in the adsorption and removal of chromium- and arsenic-based oxoanions in water. Structural modulations in iCONs were found to alter the guanidinium acidity, thus regulating the oxoanion uptake limits via ion exchange. The hydrogen bonding, steric, and electrostatic interactions at/near the guanidinium-based anion binding site in iCONs exerted heavy influences on the uptake efficiency and selectivity of arsenate but not on those of chromate. Further analyses revealed that the parallel bidentate hydrogen bonding interactions play a key role in the weak binding of arsenate to the protonated/positively charged guanidine motifs, whereas the strong ion–ion interactions between chromate and guanidinium appear to be more tolerant to the geometric and structural perturbation.

Guanidine-Based Covalent Organic Frameworks: Cooperation between Cores and Linkers for Chromic Sensing and Efficient CO2 Conversion

“…XPS was used to monitor the protonation and deprotonation processes (Figures and S9). It has been reported that condensation between TG Cl and di- or tricarboxaldehyde led to ionic COFs with protonated guanidinium units and chloride counteranions. − The photoelectron signal of Cl – was not observed for the as-synthesized TG-DMPZ but appeared in the spectrum of the HCl-acidified sample. The results suggest that TG-DMPZ was synthesized as a neutral COF and that acidification led to an ionic one with guanidinium groups.…”

Rapid and Efficient Removal of Diverse Anionic Water Contaminants Using a Guanidium-Based Ionic Covalent Organic Network (iCON)

“…Further, it was observed that the adsorption capacity of iCON-5 diminished to the greatest extent upon exposing it to an aqueous environment with pH 10 or more. This could be attributed to the partial loss/neutralization of the positive charge on the surface of iCON-5 in the presence of a high concentration of hydroxide ions at pH greater than 10. , The enthalpy of adsorption is an important parameter to evaluate the adsorption property relationship. In this regard, we performed kinetic experiments of MnO 4 – adsorption on iCON-5, and the enthalpy of hydration was estimated using the formulas mentioned in the Experimental Section.…”

Super-fast iodine capture by an ionic covalent organic network (iCON) from aqueous and vapor media

“…In this context, ionic covalent organic networks are an emerging class of functional materials that are deliberately incorporated with ionic interfaces for inducing strong and attractive interactions with oppositely charged species. [54][55][56][57][58][59][60] Herein, we report the design and synthesis of an ionic covalent organic network (iCON-4) decorated with ionic functionalities and imine linkages for superior interaction with iodine. A Schiff-base polycondensation reaction was applied to obtain iCON-4 without using any acid or metal catalyst.…”