<p>This study reports the development of Ce-doped ZnO@GO nanocomposites (ZnO:Ce@GO) with tunable defect structures for enhanced visible-light-driven photocatalytic and antibacterial performance. ZnO nanoparticles doped with 3&#xa0;mol.% Ce were integrated with graphene oxide (GO) at controlled loadings (0-6&#xa0;wt.%), forming defect-rich heterostructures with improved interfacial charge-transfer pathways. Structural and surface analyses confirm effective Ce incorporation into the ZnO lattice and strong interfacial coupling with GO, while x-ray photoelectron spectroscopy (XPS) results reveal the modulation of Ce⁴⁺/Ce³⁺ redox states and oxygen vacancy concentrations governing the electronic structure. The incorporation of GO enhances surface functionality and electron mobility, leading to improved adsorption affinity and charge transport behavior. Ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS) analysis shows an apparent redshift, which is attributed to defect-induced band-tail states and interfacial electronic interactions rather than intrinsic bandgap modification. Photocatalytic degradation of tetracycline (TC) follows pseudo-first-order kinetics under visible-light irradiation, whereas the dark-stage adsorption is better described by a pseudo-second-order model. The optimized ZnO:3%Ce@6%GO composite exhibits significantly enhanced performance (88.89% removal after 315&#xa0;min; <i>k</i>_app = 4.73 × 10⁻³&#xa0;min⁻¹), approximately 2.4 times that of pristine ZnO. The improved activity is attributed to the synergistic interaction between Ce-induced defect trapping and GO-mediated electron transport, which effectively suppresses charge recombination and promotes the generation of reactive oxygen species (^·OH, ^·O₂⁻). Importantly, the enhancement arises from a cooperative interaction between defect-mediated charge trapping and GO-enabled electron transport, rather than from individual contributions of each component. In addition, the composite demonstrates notable antibacterial activity against <i>Citrobacter</i> sp., indicating its multifunctional capability. Comparative analysis with recent ZnO-based systems suggests that this co-engineering strategy provides a more effective pathway for regulating charge-carrier dynamics than conventional single-modification approaches. These findings highlight a mechanistically supported and potentially scalable strategy for the design of advanced ZnO-based photocatalysts for antibiotic removal and antimicrobial applications.</p> Graphical Abstract <p></p>