The in situ photocatalytic oxidation of aromatic alcohols to aldehydes by air under visible-light-driven condition is an attractive and beneficial route regarding environmental crises and worldwide energy economy. Herein, CuOmelem-heteropolyacid nanophotosensitizer is disclosed as an efficient heterostructured nanocomposite involving H 5-n PW 10 V 2 O 40 nÀ … (melem-NH 3 + ) n ionic liquid, successfully prepared via a facile and straightforward procedure.This nanocomposite is characterized employing routine techniques such as Xray diffraction (XRD), Fourier transform infrared (FT-IR), diffuse reflectance spectra (DRS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM),and Brunauer-Emmett-Teller (BET). The resultant nanocomposite exhibited superior photocatalytic efficacy than its pristine melem, HPA, and CuO constituents in the in situ photo-oxidation of benzylic alcohols and in the fast condensation with o-phenylenediamine to generate a range of 2-substituted benzimidazoles, as important precursors in the synthesis of important pharmaceuticals under the illumination of a green laser light (λ 535 nm). This study suggests a radical pathway involving reactive species such as •O 2 À and OH• together with h + in a photocatalytic process. Stability and reusability experiments along with hot filtration test ensured sufficient reproducibility of the nanophotocatalyst in the reaction medium. At the final part of this study, the in vitro cellular cytotoxicity of CuO-melem-heteropolyacid nanohybrid material was evaluated on A549 human lung cancer cell line with the MTT assay.The distinct reduction in cell viability affirmed cytotoxicity of the nanomaterial against the performed cell line.