The objective of this study was to investigate the changes in the optical and surface properties of crystalline silicon and porous silicon as a result of their interaction with hydroxyl radicals. In the initial stage, the change in the interfacial free energy of crystalline silicon and porous silicon was analyzed through contact angle measurements. These measurements indicated that, for these substrates, an increase in the degree of hydrophilicity of the surface occurs in every instance. However, when the substrates were immersed in Fenton solution and hydrogen peroxide electrochemically generated (electro-Fenton process), there was a more significant variation in the hydrophilic property within a short period of time. The changes in the photoluminescence spectra of porous silicon were also analyzed with various media. For the porous silicon/Fenton system, a decrease in intensity and a shift of the PL to longer wavelengths was observed. These changes were attributed to a change in the nature of the surface functional groups on the substrate from porous silicon hydrogen-terminated to hydroxyl-terminated when the surfaces were exposed to Fenton solution. Finally, the charge collection efficiency was studied via intensity-modulated photocurrent spectroscopy, and intensity-modulated photovoltage spectroscopy. These experiments provided information about the fraction of the substrate charge carriers that do not participate in the recombination process.