In recent times, there is a mammoth challenge for the world and mankind to deal with the frequent use and misuse of antibiotics and its casual discard to the water bodies. The scavenging degradation of antibiotics which are no longer in use from the environment is a growing concern and compulsively needs to be addressed. Herein, we have devised a novel and green protocol for the synthesis of Cu 2 O decorated on reduced graphene oxide (Cu 2 O/RGO) nanocomposite (NCs) using agro-waste, i.e., orange pomace extract (OPE) as a reducing and stabilizing agent for the degradation of antibiotic. The biogenically synthesized Cu 2 O/RGO NCs proved to emerge as an excellent degradation catalyst exhibiting efficiency of 98.68% within 15 min and 86.38% within 30 min for 10 mg/L DC concentration assisted by ultrasound waves and solar light respectively in separate reactions. The complete degradation process followed a pseudo-first-order kinetics with a rate constant of 0.29 min − 1 and 0.0542 min − 1 for sonocatalytic and photocatalytic degradation process, respectively. Surface area analysis showed that with the increase in the GO amount, the doxycycline degradation increases. An in-depth mechanistic account of sonocatalytic and photocatalytic process has been discussed followed by a radical scavenging test which validated the major role of the synthesized NCs in the degradation of DC. The extraordinary catalytic indulgence of biogenically synthesized graphene-based nanocatalyst opens newer avenues for future research in green chemistry and catalytic field. Graphical abstract Supplementary Information The online version contains supplementary material available at 10.1007/s10668-022-02895-2.

The presence of silver ions at toxic concentrations in wastewater has provoked many scientists to design novel methods to detect silver ions in water. Employing agro‐waste to design nanomaterials has incited the use of orange pomace to design fruitful and biocompatible nanomaterials for endorsing sustainable and green methods. Herein, we report a sensitive and selective colorimetric detection of silver ions employing biogenically synthesized Cu2O/ZnO nanocomposites (NCs). The Cu2O/ZnO NCs were fabricated using orange pomace (OP) holistically acting as a stabilizing and reducing agent. Sensing ability of Cu2O/ZnO NCs synthesized via greener route for the presence of different metal ions such as Na+, Ca2+, Cd2+, Sr2+, Ag+, Ni2+, Fe2+, Pb2+, Mg2+, and K+ has been examined at room temperature. A naked eye colour change form slight yellowish to black was noticed in case of silver ions, this is confirmed by the shifting of maximum wavelength from 453 nm to 362 nm. Thus, in this work Cu2O/ZnO NCs was demonstrated as an extremely specific and selective colorimetric nanosensor for silver ions in water and showed a good linearity over the range of 20 μM–2 mM and a limit of detection (LOD) of 13.1 μM. The green fabrication of nanosensor for silver ions further maintain the sustainability of environment and encourage the researchers for greener fabrication of colorimetric sensors.