Semiconductor nanoparticles have optical and electrical properties that vary as a function of the particle size. The variability of these properties allows the nanoparticles to be tailored for specific applications, such as nano-electronics, photoluminescence, biological markers and, in our case, photocatalysis. By adjusting the particle size, the opto-electrical properties can be tuned to have a suitable band gap and electric potential to drive the water-splitting reaction and other photoelectrochemical reactions. Our research focuses on using ionic liquids (ILs) to synthesise and stabilise nanoparticles of CdS, the typical semiconductor for studying the opto-electrical properties of nanoparticles. The CdS nanoparticles were prepared employing a low temperature synthesis procedure from simple precursors, using butylimidazolium-based ([BMIM][anion]) and tetrabutylammonium-amino-acid-based ([TBA][amino acid]) ILs. The nanoparticles were then immobilised in propylthiol-functionalised SBA-15 to prevent aggregation. They were platinised and then tested for the photocatalytic generation of hydrogen from an aqueous sulfide/sulfite sacrificial solution under the irradiation of a mercury lamp, with the irradiation spectrum controlled by a set of water-cooled cut-off filters (305, 395 and 430 nm). As shown in the figure, the hydrogen formation rates were found to be dependent upon the IL used in the synthesis, and were substantially greater than the commercial CdS. Preliminary quantum yield calculations (defined as H2 formed per photon) using actinometry showed that our best sample, CdS synthesised from the IL [BMIM][N(CN)2] achieved nearly 3%. This quantum yield was achieved under catalytic conditions that were not mass-transfer-limited, i.e. in a regime of a large excess of water and photons. Still much higher quantum yields can be achieved in mass-transfer-limited regimes (i.e. when using much greater catalyst reactor loadings).