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Herein, we demonstrate a microwave-assisted chemical reduction technique to exfoliate a few layers of graphene from the natural waste material, ‘coconut shell’. The microwave irradiation coconut shell is subjected to structural, morphological and functional groups characterization methods including SEM, Raman, FTIR and XPS spectroscopic analyses. The formation of biomass reduced graphene (BRG) has been confirmed through Raman and FTIR spectroscopic analyzes with the presence of D, G and 2D and other functional spectral bands, respectively. The surface topography of the BRG exhibits two-dimensional mat structures with wrinkle topography, imaged by electron microscopic techniques. The metallic behaviour of the BRG is evaluated by band structure calculation using density functional theory. The synthesized nanostructure has been evaluated for exhaled diabetic breath sensing application by fabricating sensor device on the paper-based substrate by roll-to-roll coating technique. The BRG sensor exhibited enhanced sensing response at a very lower concentration of diabetic biomarker with long term stability and rapid response/recovery time of 1.11 s/41.25 s, respectively. Based on our findings, the microwave-assisted BRG is a potential candidate for fabricating highly scalable, inherently safe, economically viable and excellent sensing performance to detect exhaled diabetic breath at room temperature. [ABSTRACT FROM AUTHOR]

• Ag 2 S-Graphene based hybrid nanostructure showed remarkable hydrogen sensing performance at room temperature. • The microwave assisted hydrothermal synthesis approach provides highly scalable Ag 2 S-Graphene based hybrid nanostructure. • The Ag 2 S-Graphene based hybrid sensor proved better sensing response of 45.5% at room temperature. Herein, we aimed to synthesize an efficient room-temperature gas sensor using biomass-derived graphene nanosheets-Ag 2 S based hybrid nanostructure by a microwave-assisted hydrothermal method. The electron micrographs of the synthesized Ag 2 S-GNS nanostructure depicts rice-shaped Ag 2 S nanoparticles impregnated onto graphene surfaces. Interestingly, the bandgap of Ag 2 S and Ag 2 S-GNS based hybrid nanostructures were identified to be 2.04 eV and 1.75 eV, respectively. The Ag 2 S-GNS based hybrid nanostructure showed better hydrogen sensing efficiency than the pure Ag 2 S nanoparticles. The maximum response of 45.5 % for 150 ppm exposure of hydrogen gas was obtained for Ag 2 S-GNS based hybrid nanostructure at room temperature. The sensing response and recovery of Ag 2 S-GNS hybrid nanostructures towards hydrogen gas were found to be 19 sec and 31 sec, respectively. The high gas sensitivity and fast response time of the hybrid sensor were due to assorted attributes and synergetic effect between Ag 2 S and GNS hybrids. [ABSTRACT FROM AUTHOR]