Eco-friendly preparation of Bi2O3, Ag-Bi2O3 and Ag-Bi2O3-rGO nanomaterials and their photocatalytic H2 evolution, dye degradation, nitrite sensing and biological applications

[Display omitted] •Citrus limon mediated efficient photocatalyst such as Bi2O3, Ag-Bi2O3, & Ag-Bi2O3-rGO were prepared.•Ag-Bi2O3-rGO composite displayed excellent photocatalytic activity for hydrogen generation.•Ag-Bi2O3-rGO composite exhibited comparatively superior MB dye degradation activity.•Ag-Bi2O3-rGO modified GCE exhibited a perceptible electrochemical nitrite sensing property.•Ag-Bi2O3-rGO showed superior biological activities. The current studies demonstrate the preparation of Bi2O3, Ag-Bi2O3, Ag-Bi2O3-rGO nanocomposite using a clear and concise, environmentally sustainable, low-cost green combustion method employing citrus limon as fuel. The synthesised materials were characterised through XRD, UV-DRS, FT-IR, TGA, TEM, SEM and Raman studies. The synthesised Ag-Bi2O3-rGO composite exhibited much improved photocatalytic H2 evolution activity (432.7 μmolg-1h−1) which is 5.5 times greater than bare-Bi2O3 (78.6 μmolg-1h−1) and 4.2 times greater than Ag-Bi2O3 (101.2 μmolg-1h−1) NPs. Further, Bi2O3, Ag-Bi2O3 and Ag-Bi2O3-rGO composite degraded the MB dye by 63.96, 74.9 and 100 % respectively in 90 min. Ag-Bi2O3-rGO exhibited superior electrochemical nitrite sensing property (with the LOD of 19.792 μM). Ag-Bi2O3-rGO nanocomposite exhibited potential antiradical property with IC50 of 900 μg/mL Ag-Bi2O3-rGO was found to have potent direct haemolytic, anticoagulant, antiplatelet and antibacterial activities. This study illustrates a simple, environmental friendly green synthetic technique for large-scale synthesis of multifunctional Ag-Bi2O3-rGO nanocomposite.