Presentation Information
[3K0501-03-02]Coexisting Ion Effects on PFOA Removal via In Situ Zn/Al-LDH Coprecipitation: Experimental and DFT Analysis
○Yafan Wang1[Student presentation: Doctoral course], Yusuf Olalekan Zubair1, Chiharu Tokoro1,2 (1. Waseda University, 2. The University of Tokyo)
Chairperson: ジョン サンヒ（秋田大学）、パク イルファン（北海道大学）
Keywords:
PFOA,Layer double hydroxide,In situ method,Coexisting ions,Density functional theory calculations.
Perfluorooctanoic acid (PFOA), a persistent per- and polyfluoroalkyl substance, is repeatedly detected in Japanese landfill leachate at 6000–8000 ng/L, far exceeding the 50 ng/L guideline. In real leachate, coexisting ions can strongly perturb interfacial reactions and alter PFOA removal. Layered double hydroxides (LDHs) are promising adsorbents and can be generated efficiently via in situ coprecipitation. However, most prior work focuses on ex situ adsorption with preformed LDHs or simplified ion backgrounds, leaving it unclear how multicomponent ions regulate PFOA capture during the in situ process. Here, we systematically elucidate the effect of coexisting ions on PFOA removal via in situ Zn/Al-LDH and interpret molecular–level interactions using density functional theory (DFT). Batch tests were conducted at 5 mg/L PFOA (pH 7.5, Zn/Al = 2) with representative anions (F⁻, Cl⁻, H(BO)₄⁻, CO₃²⁻, SO₄²⁻) and cations (K⁺, Ca²⁺, Mg²⁺) over ion/PFOA molar ratios of 10–100. The in situ process achieved 88.8% removal without adding ions. Coexisting anions showed three characteristic behaviors: (i) CO₃²⁻ caused the strongest inhibition, decreasing removal to 17.46–55.86% as ratios increased. (ii) SO₄²⁻, Cl⁻, and H(BO)₄⁻ produced moderate inhibition, converging to 35.47–42.68% removal at high ratios. (iii) F⁻ showed a dual role, enhancing removal to 97% at low ratios (≤20), and shifting to suppression at higher ratios (≥50), reducing to 43.22%. Coexisting cations inhibited performance at varying ratios (55.66–68.70%). DFT results revealed that CO₃²⁻ bound substantially more strongly than PFOA, preferentially occupying reactive sites, whereas the weaker adsorption energies of SO₄²⁻, Cl⁻, and H(BO)₄⁻ led to moderate suppression. In contrast, despite strong F⁻ binding, DFT showed fluoride-incorporated LDH strengthened PFOA adsorption with a lower energy barrier, matching enhanced capture at low F⁻ levels. Overall, this work links ion-specific trends to molecular-scale energy comparison, guiding in situ LDH design for PFOA removal in ion-rich leachate.