The application of Nb2O5 in photocatalysis has sparked interest due to its potent oxidation capabilities and eco-friendly properties. However, challenges such as poor visible light response, limited reactive active sites and rapid charge recombination still hinder its practical use. Herein, a novel approach introduces elemental I-doped Nb2O5 (INO) catalyst with a three-dimensional crosslinked structure formed by ultrathin nanosheets, for the first time. This pioneering approach results in the INO catalyst with a high specific surface area (98.51 m2 g−1), abundant active sites, and enhanced visible light absorption. The dispersion of elemental I within the Nb2O5 lattice promotes the presence of delocalized electrons and improves charge carrier mobility, leading to superior catalytic performance for the degradation of diclofenac (DCF). During a 75-min period, the degradation efficiency of INO catalyst to diclofenac was found to reach 91.5 %, with a corresponding rate constant of 35.0 × 10−3 min−1. Furthermore, the study investigates the DCF degradation pathway and the toxicity changes in its byproducts. This innovative research opens new avenues for enhancing the visible light catalytic activity of Nb2O5 catalysts.