Morphological transformation of calcium phenylphosphonate microspheres induced by micellization of γ-polyglutamic acid

Abstract

The γ-polyglutamic acid (γ-PGA), an anionic homo-polyamide similar to naturally occurring polyaspartic acid in mollusk shells, is selected for morphosynthesis of calcium phenylphosphonates. It has been found that they exhibit a series of interesting morphological transformation with changing γ-PGA amount and initial pH. A rare, reversible transformation between solid and hollow microspheres, in particular, is observed. Systematic investigation suggests, for the first time, that γ-PGA exhibits the “schizophrenic” micellization behavior in response to structural and morphological changes caused by spontaneous hydrophobic modification with phenylphosphonic acids and calcium ions. The present work introduces a new paradigm for biomimetic synthesis. The results not only bring insight into the template mechanism of biomacromolecules from spontaneous hydrophobic modification, but also provide a universally applicable strategy for morphosynthesis of metal phosphonates containing hydrophobic groups. In addition, solid and hollow calcium phenylphosphonate microspheres with hierarchical structures are excellent adsorbents in the removal of aqueous lead ions. They consistently exhibit 100% Pb2+ removal efficiency when Pb2+ concentration is not more than 600 mg L−1 and even after four recycles, making them promising candidates as efficient and reusable adsorbents.