Micrometer-sized structures consisting of TiO2 nanoparticles were prepared using the sol-gel technique in combination with the structure-directing agent triethanolamine (TEA). The interaction of the TEA with the hydrolyzed sol-gel products led to the formation of TEA titanate complexes, which then enabled the assembly of sol-gel-precipitated nanosized powders. A subsequent thermal treatment of these powders resulted in the formation of micrometer-sized structures consisting of TiO2 anatase and rutile nanoparticles. To characterize the prepared powders, FTIR spectroscopy, XRD analysis, the Brunauer-Emmett-Teller method (s(BET)), UV-Vis spectrometry and electron microscopy (FE-SEM, and TEM) were employed. The photocatalytic degradation of the azo dye known as methylene blue was monitored under UV and Vis irradiation and showed that the micrometer-sized structures consisting of TiO2 nanoparticles exhibited a similar photocatalytic activity to submicrometer-sized structures consisting of TiO2 nanoparticles prepared without TEA.