Colored dyes are major sources of environmental pollution. Mineralization using heterogeneous catalysts is the method to remove such environmental pollutants. Herein, a green approach is used to prepare the nanocomposites, in which pulsed laser ablation of liquid (PLAL) is used. The synthesis of a ternary nanocomposite of ZnO/CuO/Al2O3 as a photocatalyst to degrade methylene blue (MB) dye is performed in an optimized ratio of 3:1:1 at pH = 10.37. To evaluate the structural, morphological, and optical features of the synthesized ternary nanocomposite, XRD, Raman spectroscopy, scanning electron microscopy (SEM), EDS, atomic force microscope (AFM), and UV–vis spectroscopy are used. The XRD pattern confirms that the ternary nanocomposite is highly crystalline in nature. The Raman spectra confirm the formation of the ternary ZnO/CuO/Al2O3 heterostructures. The AFM images of the ratio 3:1:1 show less agglomeration than the 1:3:1 and 1:1:3 ratios. The SEM images show agglomerated spheroids with rice-like morphologies and a mean particle size of around 40 nm. The energy bandgap (Eg) values lie in the UV region at 5.05, which means that the photocatalyst has enhanced its photocatalytic activity under sunlight. The degradation efficiency of 3:1:1 at pH = 10.37 achieves the highest value of 98.55% with a rate constant of 0.2265 min−1 after 15 min of illumination. [ABSTRACT FROM AUTHOR]