One Precursor, Two Different Outcomes: SnO-Graphite Composite and Anion-Doped SnO₂ with Ester Surface Functionality

The technological importance of SnO₂ and SnO has invited scientists to explore various aspects, including their synthesis in the nanosize regime, surface functionalization, and composite formation. In the present work, a binuclear Sn₂-EDTA complex has been demonstrated to produce a SnO-graphite composite and C, N-codoped SnO₂ nanocrystals with ester functionality in quantitative yields by thermal and solvothermal dissociation processes. The products were characterized extensively. While SnO in the SnO-graphite composite exhibited tetragonal symmetry, graphitic carbon had defects. The composite had 12 wt % of graphitic carbon. The role of the SnO-graphite composite as an anode in lithium-ion batteries (LIB) has been evaluated. Solvothermal dissociation of the Sn₂-EDTA complex in a propylene glycol medium yielded nanocrystalline SnO₂ with yellow color. Agglomerated crystallites had ester functionality on their surfaces. The surface functionality was thermally stable up to 200 °C, and its complete removal yielded tetragonal white-colored SnO₂. Co-doping of carbon and nitrogen in yellow SnO₂ reduced its optical band gap (2.9 eV). Despite the negative surface charge of the functionalized SnO₂, its affinity to rapidly adsorb anionic azo dyes (Congo red and Eriochrome black T) from aqueous solutions has been validated. Following pseudo-second-order kinetics, adsorption data analysis revealed chemisorption as the primary driving force in this process.