Interfacial anion engineering of nickel–iron layered double hydroxide/nickel foam for capture and carbonate-induced release of metal–cyanide complexes

초록

Interfacial engineering of layered double hydroxides (LDHs) provides a tunable pathway for controlling anion-exchange reactivity; however, the role of interlayer energetics in adsorption mechanisms remains insufficiently understood. Here, nickel–iron LDHs (NiFe-LDHs) were directly electrodeposited onto three-dimensional nickel foam to construct a binder-free interfacial platform for the removal of tetracyanonickelate (Ni(CN)<inf>4</inf>2−), a stable coordination complex prevalent in electroplating wastewater. By tailoring interlayer anions (SO<inf>4</inf>2−, Cl−, NO<inf>3</inf>−), we reveal that adsorption behavior is governed not by surface area but by anion-dependent energetic accessibility of the interlayer region. Among the prepared adsorbents, NiFe-NO<inf>3</inf>− exhibited the highest uptake capacity (qₑ = 14,072.84 mg/g), facilitated by weak host–guest affinity and enhanced gallery charge compensation. Kinetic and diffusion analyses confirmed a transition in adsorption pathway from film-diffusion limitation (NiFe-SO<inf>4</inf>2−) to interlayer-driven anion exchange (NiFe-NO<inf>3</inf>−). The adsorption selectivity of NiFe-NO<inf>3</inf>− was further validated in simulated electroplating wastewater containing competitive ions (CN−, SO<inf>4</inf>2−, NO<inf>3</inf>−, Cu2+, Zn2+). A carbonate-triggered relaxation strategy enabled controlled displacement of (>99 %) intercalated Ni(CN)<inf>4</inf>2−, yielding a stabilized NiFe-CO<inf>3</inf>2− phase that resists re-adsorption and enables safe releasing. This study establishes interlayer energetic control as a rational framework for designing advanced anion-exchange materials for selective removal of strongly coordinated toxic anions. © 2024

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