Display omitted •Cu2O nanoclusters using onion waste extract (Allium cepa) were synthesized.•Heterojunction between “green” Cu2O and TiO2 exhibited a bandgap of 2.80 eV.•Green Cu2O/TiO2 showed superior performance to catalyze glycerol photoreforming.•Green heterojunction chemically stable, even after recycling no Cu2+ was evident. A rapid and sustainable route for synthesizing a green photocatalyst based on nanometric Cu2O clusters dispersed on TiO2 (≈ 2 wt%) was developed. These nanoclusters were synthesized using reducing sugars (0.85 wt%) from aqueous onion waste (Allium cepa) as reducing and stabilizing agent. All this under microwave irradiation. Green photocatalysts produced hydrogen through glycerol photoreforming, ca. 4.7 mmol H2/gcat. The recyclability and reusability of these materials were demonstrated and the achieved heterojunction between Cu2O and TiO2 exhibited a bandgap within the visible spectrum at 2.80 eV, showing potential feasibility to solarize this process.