Pb contamination in aquatic environments causes severe pollution; therefore, harmless absorbents are required. In this study, we report a novel synthesis of whitlockite (WH, Ca₁₈Mg₂(HPO₄)₂(PO₄)₁₂), which is the second most abundant biomineral in human bone, and its application as a high-performing Pb²⁺ absorbent. Hydroxyapatite (HAP) and WH are prepared via a simple precipitation method. The Pb²⁺ absorption performance and mechanism of the synthesized biominerals are investigated in aqueous solutions at neutral pH. The results demonstrate that WH exhibits an excellent Pb²⁺ absorption capacity of 2339 mg g⁻¹, which is 1.68 times higher than the recorded value for HAP. Furthermore, the absorbed Pb²⁺ ions are recycled into high-purity PbI₂. This is employed as a precursor for the fabrication of perovskite solar cells (PSCs), resulting in a conversion efficiency of 19.00% comparable to that of commercial PbI₂ powder (99.99% purity). Our approach provides an efficient way to remove Pb²⁺ ions from water and reuse them in the recycling of PSCs.

In spite of a continuous increase in their power conversion efficiency (PCE) and an economically viable fabrication process, organic-inorganic perovskite solar cells (PSCs) pose a significant problem when used in practical applications: They show fast degradation of the PCE when exposed to very humid environments. In this study, the stability of PSCs under very humid conditions is greatly enhanced by coating the surface of the PSC devices with a multi-layer film consisting of ultrahydrophobic and relatively hydrophilic layers. A hydrophobic composite of poly(methyl methacrylate) (PMMA), polyurethane (PU), and SiO₂ nanoparticles successfully retards the water molecules from very humid surroundings. Also, the hydrophilic layer with moderately PMMA captures the residual moisture within the perovskite layer; subsequently, the perovskite layer recovers. This dual function of the coating film keeps the PCE of PSCs at 17.3% for 180 min when exposed to over 95% humidity.