Iron coral: Novel fungal biomineralization of nanoscale zerovalent iron composites for treatment of chlorinated pollutants

In this research, a facile fungal biomineralization method was developed for the synthesis of nanoscale zerovalent iron (nZVI) with a unique N-doped branching structure, which showed excellent stability and mediated high degradation of carbon tetrachloride (CCl₄) in aqueous solution. The ureolytic fungus Neurospora crassa was cultured in medium containing Fe²⁺ and urea which resulted in iron carbonate biomineral precipitation. Following carbonization at 900 °C, the fungal-carbonate composite became highly porous and granular nanoparticles (~50 nm diameter) were distributed evenly around the carbonized hyphae in a coralline manner. This ‘iron coral’ composite was identified as a mixture of zerovalent iron (Fe⁰), carbon iron (Fe_1.91C_0.09) and iron oxide (Fe₃O₄). The porous branching hyphal framework improved the capture efficiency of CCl₄, and the N-doped sites may accelerate the electron transfer between CCl₄ and nZVI. Geochemical simulation was applied to verify the formation of the biominerals, and chemical analyses confirmed its significant degradation ability for CCl₄. These findings have therefore demonstrated that ureolytic fungi can provide a promising environmental-friendly system for the novel preparation of nZVI through biomineralization with the resulting ‘iron coral’ capable of significant removal of a chlorinated compound and therefore indicating new bioremediation applications.