The gelation of a low value-added industrial waste, phenolic oil (PO), was successfully carried out for the first time in the presence of an acid catalyst and paraformaldehyde (PF), which is a by-product of the formaldehyde industry. Therefore, the use of PO and PF can be considered a win-win situation and as an attempt to valorise these 'wastes' and integrate them into a circular economy. A broad range of formulations has been explored, and the optimal preparation conditions in terms of materials' homogeneity and yield have been identified for gels dried in different ways, leading to xerogels, cryogels and aerogels, as well as to their carbonaceous counterparts after pyrolysis at 900°C. The porous textures of the latter materials were studied in depth, and the results allowed selecting one carbon xerogel for adsorption studies of a reference molecule, methylene blue (MB), in the aqueous phase. Kinetic and equilibrium measurements, as well as the calculation of associated thermodynamic parameters, allowed elucidating the detailed adsorption mechanisms of MB in this type of carbon gel.