Phosphate precursor chemistry directs the interlayer structure and U(VI) coordination of FeAl-LDH: a dihydrogen phosphate-driven design for selective uranium capture

Phosphate precursor chemistry regulates FeAl-LDH structure and U(VI) capture. • H2PO4−-derived FeAl-LDH balances site accessibility and reversibility. • U(VI) removal is dominated by inner-sphere coordination with O-donor sites. • Electrostatic enrichment and open galleries provide auxiliary enhancement. • Precursor regulation offers an alternative to conventional post-modification. Understanding how phosphate precursor chemistry regulates the structure and U(VI) capture performance of layered double hydroxides (LDHs) remains challenging, as most studies focus on phosphorus loading rather than precursor-dependent phosphate chemistry. In this work, FeAl-LDH materials were synthesized using H 2 PO 4 − , HPO 4 2− , and PO 4 3− as phosphate precursors under identical conditions to investigate their effects on interlayer structure and U(VI) adsorption. Among the three precursor systems, the H 2 PO 4 − -derived material showed the most favorable balance of pore accessibility, phosphorus‑oxygen site availability, and adsorption-desorption reversibility. ICP-OES results further showed that higher phosphorus incorporation did not correspond to higher U(VI) uptake, indicating that adsorption performance depends more strongly on the chemical environment and accessibility of phosphate-derived sites than on phosphorus loading alone. The optimized FeAl-LDH-P(0.3) exhibited a Langmuir-fitted theoretical maximum adsorption capacity ( q ₘ) of 1117.21 mg/g and achieved 98% U(VI) removal from uranium-tailings pore water and leachate. Mechanistic analyses indicate that U(VI) removal is dominated by inner-sphere complexation with Fe/Al-OH and phosphorus‑oxygen sites, while electrostatic pre-enrichment and enhanced mass transfer through accessible interlayer/pore channels act as auxiliary effects. These results demonstrate that phosphate precursor chemistry can regulate the final phosphate-containing environment and structure-performance relationship of FeAl-LDH for selective uranium capture. Download: Download high-res image (339KB) Download: Download full-size image