To the best of our knowledge, this study is the first to investigate the effect of chemical vapour etching (CVE) combined with copper decoration on both the optical and catalytic activities of silicon micro-particles (SiμPs). After exposure to acid vapours emanating from a hot solution of hydrogen fluoride/nitric acid (HF/HNO3), scanning electron microscope images of the treated powder show the formation of a porous, sponge-like structure on the sidewalls of SiμPs. Fourier transmission infra-red analysis shows the appearance of hydride bonds related to the formation of the porous structure. X-ray diffraction measurements and Raman spectroscopy show the good crystallinity of the samples. The strong photoluminescence properties of the obtained porous SiμPs (pSiμPs) reveal that the vapour etching process generated silicon nanocrystals within these particles. In this work, we have investigated the catalytic activity of copper nanoparticles (CuNPs) loaded on the surface of pSiμPs, in order to reduce the toxic compound 4-nitrophenol to 4-aminophenol. The results show excellent catalytic performance in very short times (less than 1 min).