Monolithic structured TiO2/aerogel composites were prepared from resorcinol-formaldehyde polymer aerogel (RFA) and its carbon aerogel (RFCA) derivative. A resorcinol-formaldehyde hydrogel was synthesized in a sol-gel reaction and transformed into polymer aerogel by supercritical drying. The RFA was converted to carbon aerogel by pyrolysis at 900 °C in dry N2.Amorphous and crystalline TiO2 layers were grown from TiCl4 and H2O precursors by atomic layer deposition (ALD) at 80 °C and 250 °C, respectively, on both RFA and RFCA. The substrates and the composites were studied by N2 adsorption, TG/DTA-MS, Raman, SEM-EDX and TEM techniques. Their photocatalytic activity was compared in the UV catalyzed decomposition reaction of methyl orange dye. Keywordsresorcinol-formaldehyde polymer aerogel, carbon aerogel, photocatalysis, ALD, TiO2 IntroductionBeside crystalline carbonaceous nanomaterials such as fullerene, graphene, graphene oxide, nanodiamond, carbon nanospheres, carbon nanotubes; mesoporous carbon aerogels have attracted a great deal of attention. Carbon aerogels, available also in monolithic form, have several favorable properties, for example they can be used as adsorbents or as substrates for catalysts, because of their robustness and high specific surface area [1,2]. They are also excellent thermal and phonic insulators, while conduct electricity. These properties can be tuned through their synthesis conditions. [3][4][5][6][7] Resorcinol-formaldehyde (RF) organic aerogels, that Pekala and co-workers synthetized for the first time [8], undergo two main stages during preparation. In the first stage a hydrogel is prepared by a sol-gel process and in the second stage after drying the aerogel is obtained. The resorcinol-formaldehyde polymer aerogel becomes a carbon aerogel in a consecutive third stage, which is carbonization occasionally followed by activation. Depending on the conditions carbonization or activation influence the structural and performance characteristics, like the specific surface area, significantly [9][10][11][12].Photocatalytic carbon nanocomposites have great potential in the field of environmental remediation, water splitting and self-cleaning surfaces [13,14]. Among the various semiconductor oxide photocatalysts TiO2 is researched widely, due to being stable and nontoxic. TiO2 has ideal band gap width for the half reactions of water splitting and its composites with other nanomaterials, such as carbon nanostructures, may enhance the photocatalytic activity. However, its use still faces some difficulties, such as a narrow light response range limited to UV. The carbon nanostructure inhibits the recombination by promoting the charge separation as an electron acceptor. This effect and the widening of the wavelength response range through Ti-O-C bonds as well as modifying the photocatalytic selectivity are three advantages of TiO2 composites [3,[15][16][17][18]. Moreover, a number of studies indicates that nanoporous or nanostructured carbon materials, such as activated carbon or graphene-oxide...