Pure ZnO and erbium (1, 3, and 5 at. %)-doped ZnO nanoparticles aerogels were synthesized by sol-gel in supercritical drying conditions of isopropanol. The aim of this work is to study the effect of erbium ions on structural, optical, and photocatalytic properties of ZnO aerogels using various physicochemical techniques. The photocatalytic degradation of methylene blue (MB) under UV light irradiation is significantly enhanced with the introduction of Er³⁺ ions into the structure. The complete degradation of MB (99%) was obtained with an optimum of 1 and 3 at. % of erbium after 100 min of UV irradiation. These results are in good agreement with those obtained by electron paramagnetic resonance (EPR) spectroscopy spin trapping measurements where the highest amount of hydroxyl radicals •OH, responsible for the degradation of methylene blue, is observed with ZnO doped with 1 and 3 at. % erbium. A decrease of the electron-hole pairs recombination rate was confirmed by photoluminescence (PL) analyses in the Er-doped samples, due to the high interactions between Er³⁺ ions which lead to an increase of the non-radiative process originated from PL quenching. Graphical abstract