<p>Growing concerns over the toxicity and environmental impact of conventional surfactants have accelerated the search for eco-friendly capping agents for nanomaterials synthesis. In this study, we have employed castor oil (CO) and ricinoleic acid (RA) as green capping and dispersing agents in the preparation of PbS nanoparticles. The synthesis was carried out via thermolysis of bis(tetrahydroquinolinedithiocarbamato)lead(II) complex at temperatures ranging from 190 to 300&#xa0;°C. The influence of the nature of the capping agent and the synthesis temperature on the morphology, structure, and optical properties of the synthesized particles was studied. P-XRD analysis demonstrated formation of crystalline, phase pure cubic rock salt PbS at all reaction conditions. Morphological characterization revealed distinct, temperature dependent evolution of particle morphologies. Castor oil-capped nanoparticles exhibited a progression in anisotropic morphologies with increasing temperature, in which a mixed population of quasi-spherical particles, nanorods, multipods, and cuboidal structures were observed at 190&#xa0;°C, while predominantly branched star-like structures were formed at higher temperatures. In contrast, ricinoleic acid capped nanoparticles displayed a transition from quasi-spherical to cuboidal and rod-like structures with increasing temperature, which reflects a balance between kinetic and thermodynamic growth pathways. UV-Vis-NIR spectra of all the synthesized particles were blue shifted relative to bulk PbS, with Tauc analysis yielding direct band gaps in the range of 1.125–0.816&#xa0;eV, confirming the synthesis of nanoscale PbS. This study highlights the potential of both castor oil and its major fatty acid component, ricinoleic acid, as renewable, biodegradable, and environmentally benign capping and dispersing agents for the green synthesis of PbS nanoparticles.</p> Graphical abstract <p></p>