Binding and Removal of Sulfate, Phosphate, Arsenate, Tetrachloromercurate, and Chromate in Aqueous Solution by Means of an Activated Carbon Functionalized with a Pyrimidine-Based Anion Receptor (HL). Crystal Structures of [H₃L(HgCl₄)]·H₂O and [H₃L(HgBr₄)]·H₂O Showing Anion−π Interactions

Abstract

Binding of anions of great environmental concern such as SO(4)(2-), PO(4)(3-), AsO(4)(3-), HgCl(4)(2-), and CrO(4)(2-) by the protonated forms of a tren-like (tren = tris(2-aminoethyl)amine) ligand (HL) functionalized with a pyrimidine residue was studied by means of potentiometric measurements and isothermal titration calorimetry (ITC) affording log K, ΔH°, and TΔS° values for the formation of the relevant complexes. The complexes show high to very high stability due to the particular topology and electronic properties of the ligand which is able to use two separated coordination environments to host the anions, the protonated tren site where electrostatic and hydrogen bond interactions are operating, and the pyrimidine ring which may act via anion-π interaction. A contribution of -8.9 ± 0.4 kJ/mol for pyrimidine-anion interaction in water was derived for SO(4)(2-) binding. The crystal structures of [H(3)L(HgCl(4))]·H(2)O (1), [H(3)L(HgBr(4))]·H(2)O (2), and that previously reported for [H(3)L(CdI(4))], clearly show these binding features in the solid state. A hybrid AC-HL material obtained by adsorption of HL on commercial activated carbon (AC) was used to study the removal of these anions from water. AC-HL shows enhanced adsorption capacity toward all the anions studied with respect to AC. This behavior is ascribed to the stronger interaction of anions with the HL function of AC-HL than with the Cπ-H(3)O(+) sites of the unfunctionalized AC.

Binding and removal of octahedral, tetrahedral, square planar and linear anions in water by means of activated carbon functionalized with a pyrimidine-based anion receptor

“…2). 11,17,18 In particular, the H 4 L[Co(CN) 6 ] complex showed one of the strongest anion-p interactions so far reported. 17 While in H 3 L 2+ protonation involves the two primary amine groups of the tren moiety, in H 4 L 3+ also the pyrimidine nitroso group is protonated.…”

“…11,24 AC is a graphitized activated carbon with a surface area of 1062 m 2 g À1 and containing oxygen as the only heteroatom component present in signicant amount (3.9%). 11,24 Most of the surface area (ca. 1000 m 2 g À1 ) is associated to narrow micropores (diameter < 2.5-3.0 nm) whereas the remaining area corresponds to mesopores (2.5-3 nm < diameter > 50 nm) and macropores (diameter > 50 nm).…”

Preparation and characterization of trihydroxamic acid functionalized carbon materials for the removal of Cu(II) ions from aqueous solution

“…The surface charge density (Q in mmol of protons/g of adsorbent) of the materials was determined by a method based on potentiometric titration data [44][45][46], following a reported procedure [28,30] and by using KOH 0.1 M as titrating agent. The proton isotherms were then obtained by plotting Q vs the equilibrium pHs.…”

“…For this reason, the control of the surface chemical functionalization of ACs without changing their textural properties [23] becomes a main objective in order to obtain efficient and selective carbon materials for metal ion recovery. We have reported a functionalization method of carbon materials [24][25][26][27][28][29][30] materials [31]. The procedure results in carbon/receptor hybrid materials.…”

Method To Characterize Acid–Base Behavior of Biochar: Site Modeling and Theoretical Simulation

“…In addition, a basic site corresponding to pK a = 7.02 on a low-functionalized activated carbon was considered as arene centers (Cπ site). 43 On the other hand, a theoretical calculation suggested that pK a of pyrones varied in a large interval (0−12). 39 The pK a values of basic sites obtained in this manuscript fall in the range of the basic strength mentioned above and could deepen the understanding of the versatility of the strength of basic sites on biochar surfaces.…”