How Does Competition between Anionic Pollutants Affect Adsorption onto Mg–Al Layered Double Hydroxide? Three Competition Schemes

Abstract

Competitive adsorption of three anionic orange-type dyes (i.e., methyl orange, orange II, orange G) and three inorganic anions (HPO 4 2− , SO 4 2− , CrO 4 2− ) onto Mg−Al layered double hydroxide (LDH) from bisolute aqueous solutions has been studied in view of potential application of the sorption-based technology in dye removal from textile wastewater effluents. The individual solute affinities for the LDH sample were inferred from the calorimetry measurements of the cumulative enthalpy of displacement in single-solute systems, thus leading to the following affinity order: CrO 4 2− ≈ SO 4 2− < OG 2− ≈ HPO 4 2− < OII − ≪ MO − . The individual and composite adsorption isotherms from bisolute aqueous solutions were determined by a solution depletion technique and supplemented by XRD studies on the well-defined adsorption systems corresponding to selected points on isotherms. Based on the shape of the individual adsorption isotherms for a dye and inorganic anion, it was possible to distinguish three different competition schemes: when the reduction in adsorption extent concerns mainly one of the solutes (Type I and Type III) or when this reduction applies to both solutes (Type II). The order of decreasing effectiveness of the inorganic anion in depressing the retention capacity of Mg−Al−LDH−NO 3 toward a given dye, on a perequivalent basis, was as follows: HPO 4 2− > SO 4 2− ≈ CrO 4 2− , methyl orange; HPO 4 2− > CrO 4 2− > SO 4 2− , orange II; HPO 4 2− ≈ SO 4 2− > CrO 4 2−, orange G.

Highly Efficient Sorption of Methyl Orange by a Metal–Organic Resin–Alginic Acid Composite

“…Notably, the hydrated environment around the A − anions affects their interactions with the anilinium cations. According to the simple empirical model, inorganic anions are much smaller and more hydrated than the MO − dye, with the radius r of the bare anion, average number n of water molecules in the hydration shell, and enthalpy of hydration Δ H hyd of r =0.240 nm, n= 3, Δ H hyd =−1035 kJ mol −1 for SO 4 2− , and r =0.181 nm, n= 2, Δ H hyd =−365 kJ mol −1 for Cl − …”

CuAl LDH/Rice Husk Biochar Composite for Enhanced Adsorptive Removal of Cationic Dye from Aqueous Solution

“…Table 3 presents the calculation results of the coefficient correlation, which identifies that the Langmuir model better fitted than the Freundlich model for composite material. A good fit of the Langmuir model indicates the adsorption process of the composite is monolayer with uniform energy distribution [34]. According to Meili et al [19], the Langmuir process assumed that no significant interaction between adsorbate molecules.…”

Morphological control of poly(vinylidene fluoride)@layered double hydroxide composite fibers using metal salt anions and their enhanced performance for dye removal

“…The interplanar distance of LDHs increases from 1.099 nm to 2.552 nm aer MO adsorption, which was ascribed to the intercalated MO anions. 39 This nding meant that anion exchange existed between the interlayer anions and MO anions during adsorption process. Meanwhile the adsorption also could occur on the external surface of LDHs through the electrostatic attraction and hydrogen bonds, because it exhibited positive charge and contained a lot of hydroxyl groups.…”