Plastic waste, especially polyethylene terephthalate (PET), poses a serious environmental challenge due to its widespread use and lack of effective upcycling routes. Meanwhile, hydrogen peroxide (H2O2) is an environmentally benign oxidant widely used in chemical synthesis, pharmaceutical manufacturing, and environmental remediation. In this work, waste PET was converted into a terephthalic acid (BDC) ligand, which is the feedstock for the further synthesis of high-value UiO-66-type metal–organic framework (MOF) photocatalysts by a two-stage process consisting of chemical hydrolysis followed by rapid aqueous-phase synthesis. Amino (–NH2) functional groups were successfully introduced into the MOF framework during synthesis, yielding PET-derived UiO-66-–NH2 photocatalysts with tuneable ligand compositions. The PET-derived UiO-66-based catalysts were applied for photocatalytic H2O2 production by oxygen reduction, with PET-UiO-66-NH2-50% exhibited outstanding photocatalytic performance for H₂O₂ generation, achieving a production rate of 354 μmol/g/h under visible-light irradiation using pure water as the reaction medium, without the addition of organic solvents or sacrificial agents. This activity is 2.8 times higher than that of the non-NH₂-modified PET-derived UiO-66 photocatalyst and more than three times higher than that of UiO-66 prepared from commercial BDC, highlighting the unique advantages of PET-derived linkers and amino functionalization. The enhanced performance is attributed to the synergistic effects of amino functionalization, optimized ligand composition, enhanced visible-light absorption, and improved charge separation efficiency within the PET-derived framework. This work not only demonstrates a sustainable pathway for transforming waste PET into high-performance photocatalysts but also establishes a green, sacrificial-agent-free platform for photocatalytic H2O2 production. The proposed strategy provides valuable insights into plastic waste upcycling and the rational design of environmentally friendly catalytic systems for future energy conversion and environmental remediation applications.