We combine nanochemistry and photochemistry to push photocatalysis to achieve practical uses. Nanochemistry offers the ability to produce an array of nanoparticles with a wide tunability of size, shape, composition, and optical properties. Photoexcitation of these nanoparticles gives access to various electronic states that display distinct chemical reactivity and selectivity at ambient temperature far exceeding thermally driven reactions. Uniquely to metallic nanoparticles, their strong light absorption, robust nature, recyclability, and large surface areas render them candidates as photocatalytic materials. These catalysts have the potential to harvest solar energy and conduct reactions at ambient temperature, an economically desirable condition for industrial applications.