Zinc sulfide nanoparticles (ZnS NPs) have been deposited on carbon nanotubes (CNTs) from a single source precursor, zinc(II) bis(diethyldithiocarbamate), using a one-step batch supercritical carbon dioxide (sc-CO2) process. By eliminating the need for an additional sulfur source while simultaneously employing CO2 as the solvent, this method replaces environmentally unfriendly chemicals commonly used in ZnS-CNT nanocomposite synthesis such as ethylene glycol, thiourea, and hydrogen sulfide. ZnS NP morphology displayed large clusters (209 +/- 24 nm) that were comprised of smaller particles (16.9 +/- 1.9 nm). Photoluminescence spectroscopy demonstrated broad band fluorescence of the ZnS-CNT nanocomposite at 440 nm (2.82 eV) and fluorescence of a Mn doped ZnS-CNT nanocomposite at 445 nm (2.79 eV) and 602 nm (2.07 eV), also in agreement with previous studies. The ZnS-CNT nanocomposite was compared to ZnS NPs synthesized in the absence of a substrate; results indicated that the ZnS-CNT nanocomposite was formed by a heterogeneous reaction mechanism in the sc-CO2 system.