Natural bio-sourced polymers: Emerging precursors for the synthesis of single atom catalysts

Natural bio-sourced polymers have been utilized as potential support materials and sustainable source for the preparation of doped carbon materials via high temperature heat treatment due to the presence of heteroatoms (N-, O-, P- and S) in the form of various functional groups. Moreover, free availability of these functional groups facilitates the incorporation and binding of metal ions through complexation process that is believed to be essential for the synthesis of immobilized catalysts and single atom catalysts (SACs). SACs are the key chain between homogenous and heterogeneous catalysts due to their unprecedented robustness in terms of catalytic activity and stability. Natural bio-sourced polymers have emerged as one of the irreplaceable substitutes to synthesize SACs by providing anchoring sites to the metal ions and their subsequent transformation into a carbonaceous material generating isolated metal atomic sites. The type of coordination atmosphere of single metal atom enriches catalytic activity by establishing noble interactions with the support material. The primary aim of this review article is to discuss the advancement and provide insight about the utilization of various natural bio-sourced polymers in the preparation of different metal-based SACs. Moreover, we have discussed individual steps for the synthesis of SACs and techniques required for the visualization and determining the coordination environment of single atom sites. At the end, challenges and future prospective on natural bio-sourced polymer-based SACs synthesis and other applications are deliberated.