CoO, Cu, and Ag Nanoparticles on Silicon Nanowires with Photocatalytic Activity for the Degradation of Dyes

Photocatalytic semiconductors require maintaining stability and pursuing higher efficiencies. The studied systems were silicon nanowires (Si NWs ), silicon nanowires with cobalt oxide nanoparticles (Si NWs -CoO NPs ), and silicon nanowires with copper nanoparticles (Si NWs -Cu NPs ). Si NWs were synthesized by metal-assisted chemical etching (MACE) from silicon wafers keeping the remaining silver nanoparticles for all three sample types. The nanowires were about 23–30 µm in length. CoO NPs and Cu NPs were deposited on Si NWs by the autocatalytic reduction processes (electroless). There were many factors in the process that affect the resulting structures and degradation efficiencies. This work shows the degradation of methyl orange (MO) together with the chemisorption of methylene blue (MB), and rhodamine 6G (Rh6G) by direct illumination with visible radiation. The MO degradation kinetics were in the sequence Si NWs -Cu NPs (88.9%) > Si NWs (85.3%) > Si NWs -CoO NPs (49.3%), with the Si NWs -Cu NPs having slightly faster kinetics. However, Si NWs -CoO NPs have slow degradation kinetics. The chemisorptions of MB and Rh6G were Si NWs -Cu NPs (87.2%; 86.88%) > Si NWs (86%; 87%) > Si NWs -CoO NPs (17.3%; 12%), showing dye desorptions together with lower chemisorption capacities. This work shows iridescence in optical microscopy images by the visible light interference caused by the spaces between the nanowire bundles.