Toward the design of efficient adsorbents for Hg²⁺ removal: Molecular and thermodynamic insights

Abstract

A systematic DFT study was performed to evaluate the effect of oxygenated functional groups for Hg2+ adsorption in aqueous systems. This work includes several aspects usually neglected in many current works, namely, ground‐state multiplicity, solvation effects, establishment of thermodynamic parameters, atomic charge transfer, and modeling of infrared spectra. In addition, two carbonaceous models were studied to account for both the effect of the carbonaceous matrix and the oxygenated functional groups on the Hg2+ binding. Adsorption energies indicated that Hg2+ adsorption on the unsaturated model is favored in the following order: phenol > lactone > semiquinone > carboxyl, whereas for the saturated model, the Hg2+ adsorption energy decrease order is: carboxyl > semiquinone > lactone. Thermodynamic parameters confirmed that the adsorption process is spontaneous (unsaturated model), while the infrared spectra provided an insight at the atomic level about the experimentally reported bands. Our results contributed to a deeper understanding of the current experimental information on the effect of the surface functional groups on the Hg2+ adsorption over carbonaceous materials as different active sites can be present on oxygenated carbonaceous materials for metal adsorption. The results also create new ways to improve the performance of adsorption capability of mercury and other pollutants.

Molecular Structure Analysis and Mercury Adsorption Mechanism of Iron-Based Modified Biochar

“…Analysis of the Surface Functional Groups. According to the different characteristic absorption peaks corresponding to different functional groups, 22,23 the FTIR spectra of the biochar (Figure 4) were divided into four regions: hydroxyl vibration region a (3700−3200 cm −1 ), X−H stretching vibration region b (2900−2500 cm −1 , X is C, N), double-bond vibration region c (1900−1400 cm −1 ), and fingerprint region d (1400−500 cm −1 ). The hydroxyl vibration region includes free hydroxyl groups (3650−3600 cm −1 ), bonded hydroxyl groups (3550−3200 cm −1 ), and carboxylic acid hydroxyl groups (3500−3300 cm −1 ).…”

Adsorption dynamics of Cd2+(aq) on microwave-synthetized pristine biochar from cocoa pod husk: Green, experimental, and DFT approaches

“…In previous studies, the zigzag and armchair models were used in several studies with different applications to model carbonaceous surfaces. 89 , 90 , 91 , 92 …”

“…The correct ground-state structure with the fewest spin impurities and lowest electron energy was determined by calculating the single-point energies of the starting structures in different electronic states. 89 Single-point energy is calculated at the B3LYP-D3/def2-QZVP//B3LYP-D3/def2-TZVP level of theory by adding zero-point energy (ZPE) and thermal (temperature-dependent) corrections. Adsorption energy (E ads ) of adsorbate "A" on the solid surface "B" can be calculated as follows ( Equation 25 ): where E ads is the adsorption energy, kJ/mol; E A is the energy of the adsorbent, kJ/mol; E B is the energy of the adsorbate (Cd 2+ ), kJ/mol; E AB is the total energy of adsorbate/adsorbent system in the equilibrium state, kJ/mol.…”