This study reports a clean, surfactant-free synthesis of cobalt-based nanomaterials via pulsed laser ablation in liquid (PLAL) using deionized water as the ablation medium for advanced photocatalytic applications. A high-purity cobalt metal target was irradiated with a pulsed laser under controlled conditions to generate cobalt and cobalt-oxide nanoparticles directly in aqueous media, eliminating the need for chemical reducing agents, stabilizers, or post-treatment purification. The crystalline structure, phase composition, and crystallite size of the as-synthesized nanomaterials were systematically investigated using X-ray diffraction (XRD), confirming the formation of mixed metallic cobalt and cobalt oxide phases. Transmission electron microscopy (TEM) analysis revealed the successful formation of well-dispersed, predominantly nanospherical particles with a narrow size distribution in the nanometer range. The optical absorption characteristics were examined using UV–visible spectroscopy, demonstrating strong absorption in the visible region, which is highly favorable for photocatalytic activity under light irradiation. The photocatalytic performance of the synthesized cobalt-based nanomaterials was evaluated through the light-driven degradation of a model organic pollutant in aqueous solution. The nanomaterials exhibited remarkable degradation efficiency under visible-light irradiation, which can be attributed to their enhanced light-harvesting capability, high surface-to-volume ratio, and efficient charge carrier generation. The superior photocatalytic response confirms the effective role of PLAL in tailoring the structural and optical properties of cobalt-based nanomaterials. Overall, this work highlights PLAL in deionized water as a green, scalable, and environmentally benign synthesis route for producing high-purity cobalt-based photocatalysts with promising potential for wastewater remediation and environmental purification technologies.