Heavy metal distribution and speciation in hyperaccumulators for single-atom catalyst synthesis: a review

Hyperaccumulators have made significant strides in the field of phytoremediation due to their high capacity for heavy metal accumulation, but the safe disposal and resource utilization of metal-rich biomass after harvest remain major challenges. Although significant progress has been made in the past five years in the preparation of single-atom catalysts (SACs) using hyperaccumulators as precursors, there is still a lack of a comprehensive summary of the intrinsic relationship between heavy metal migration and speciation within plants and the structural properties of SACs. In this review, we present the design, preparation, and application of hyperaccumulator-derived SACs in environmental catalysis. We first summarize the biochemical mechanisms underlying the rhizosphere activation, trans-membrane transport, and long-distance transport of heavy metals (HMs) by hyperaccumulator. Subsequently, we focus on the distribution patterns, chemical speciation, and natural coordination environments of HMs and other elements at the subcellular level. Through representative case studies, we elucidate the critical regulatory roles of the speciation and spatial distribution of HMs within hyperaccumulators in defect formation and active site formation, as well as the evolution of pore structures during pyrolysis. Finally, we discuss the key challenges and future opportunities in this field and offer prospects for the resource utilization of hyperaccumulators and the green synthesis of high-performance SACs.