Effect of anion co-existence on ionic organic pollutants removal over Ca based layered double hydroxide

The effects of co-existing anions (NO₃ ⁻ or SO₄ ²⁻) on the removal of sodium dodecylsulfate (SDS), representing anionic organic pollutants, by Ca-based layered double hydroxide (CaAl-LDH-Cl) are investigated to provide fundamental insights on the ionic surfactant removal in the presence of co-existing anions, and facilitate the establishment of a practical and advanced water treatment for environmental remediation. The SO₄ ²⁻ system shows higher adsorption capacity (4.43 mmol·g⁻¹) and larger d-spacing of adsorption resultant (3.4 nm) than the control system with no co-existing anion (3.64 mmol·g⁻¹, 3.25 nm) and the NO₃ ⁻ system (3.82 mmol·g⁻¹, 3.27 nm). The macroscopic and microscopic analyses reveal that, NO₃ ⁻ had a little influence on the SDS removal due to strong electrolysis, while SO₄ ²⁻ could significantly promote the SDS removal. Moreover, the reaction mechanism varies under different molar ratios of DS⁻/SO₄ ²⁻.