Green sustainable synthesis of Ag doped SnO2 decorated reduced graphene oxide hierarchical nanohybrid material: An excellent mesoporous catalyst for efficient reduction of nitroaromatics

A foliose lichen species, Lobaria retigera mediated environmentally sustainable, economically viable green synthesis procedure to access Ag doped SnO2 (Ag@SnO2) and hierarchical Ag doped SnO2 decorated reduced graphene oxide (rGO-Ag@SnO2) nanohybrid material is reported. Carbohydrate, a primary metabolite present in the aqueous lichen extract is presumed to be responsible for the reduction and stabilization of the nanoparticles. The nanoparticles were mostly spherical with < 5 nm sizes. The co-existence of Ag and SnO2 is validated by XRD and EDS studies. The XPS spectra revealed the +IV oxidation state of Sn. The hybrid material can efficiently catalyse reduction of toxic aromatic nitro compounds which meet most of the rigorous demands of sustainable development goals and clean technology. The reduction efficiencies of 81-91% in a time span of 2-18 minutes were achieved due to the unique hierarchic porous architecture of the ternary hybrid material. The reduction of nitroaromatics to amino-compounds were confirmed by UV-visible spectroscopy and LC-MS study. The recyclability of the catalysts were confirmed by performing repeated reduction reactions with virtually no loss of its catalytic features. BET study of the hybrid materials revealed a type IV with H-3 hysteresis loop indicating a high mesoporous nature with significant extended surface area. The dispersed Ag doped rutile-SnO2 over rGO sheet could be clearly discerned from TEM and SEM micrographs. Elemental mapping distinctly revealed the homogeneous distribution of the constituent elements in the hybrid materials