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...

Carbon nanospheres (CNSs) were prepared by hydrothermal synthesis, and coated with TiO2 and ZnO nanofilms by atomic layer deposition. Subsequently, through burning out the carbon core templates hollow metal oxide nanospheres were obtained. The substrates, the carbon-metal oxide composites and the hollow nanospheres were characterized with TG/DTA-MS, FTIR, Raman, XRD, SEM-EDX, TEM-SAED and their photocatalytic activity was also investigated. The results indicate that CNSs are not beneficial for photocatalysis, but the crystalline hollow metal oxide nanospheres have considerable photocatalytic activity.

[NH4Cu­(OH)­MoO4] as active photocatalyst in the decomposition of Congo Red when irradiated by UV or visible light has been prepared in an unusual ammonia/water ligand exchange reaction of [tetraamminecopper­(II)] molybdate, [Cu­(NH3)4]­MoO4. [Cu­(NH3)4]­MoO4 was subjected to moisture of open air at room temperature. Light blue orthorhombic [Cu­(NH3)­(H2O)3]­MoO4 was formed in 2 days as a result of an unexpected solid/gas phase ammonia–water ligand exchange reaction. This complex does not lose its last ammonia ligand on further standing in open air; however, a slow quasi-intramolecular (self)-protonation reaction takes place in 2–4 weeks, producing a yellowish-green microcrystalline material, which has been identified as a new compound, [NH4Cu­(OH)­MoO4], (a = 10,5306 Å, b = 6.0871 Å, c = 8.0148 Å, β = 64,153°, C2, Z = 4). Mechanisms are proposed for both the sequential ligand exchange and the self-protonation reactions supported by ab initio quantum-chemical calculations and deuteration experiments as well. The [Cu­(NH3)­(H2O)3]­MoO4 intermediate transforms into NH4Cu­(OH)­(H2O)2MoO4, which loses two waters and yields [NH4Cu­(OH)­MoO4]. Upon heating, both [Cu­(NH3)4]­MoO4 and [Cu­(NH3)­(H2O)3]­MoO4 decompose, losing three NH3 and three H2O ligands, respectively, and stable [Cu­(NH3)­MoO4] is formed from both. The latter can partially be hydrated in boiling water into [NH4Cu­(OH)­MoO4. This compound can also be prepared in pure form by boiling the saturated aqueous solution of [Cu­(NH3)4]­MoO4. All properties of [NH4Cu­(OH)­MoO4] match those of the active photocatalyst described earlier in the literature under the formulas (NH4)2[Cu­(MoO4)2] and (NH4)2Cu4(NH3)3Mo5O20.

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Nitrogen containing carbon aerogel was prepared from resorcinol-melamine-formaldehyde (R-M-F) polymer gel precursor. The polymer gel was supercritically dried with CO2, and the carbonization of the resulting polymer aerogel under nitrogen atmosphere at 900 °C yielded the carbon aerogel. The polymer and carbon aerogels were characterized with TG/DTA-MS, low temperature nitrogen adsorption/desorption (-196 °C), FTIR, Raman, powder XRD and SEM-EDX techniques. The thermal decomposition of the polymer aerogel had two major steps. The first step was at 150 °C, where the unreacted monomers and the residual solvent were released, and the second one at 300 °C, where the species belonging to the polymer network decomposition could be detected. The pyrolytic conversion of the polymer aerogel was successful, as 0.89 atomic% nitrogen was retained in the carbon matrix. The nitrogen doped carbon aerogel was amorphous and possessed a hierarchical porous structure. It had a significant specific surface area (890 m 2 g -1 ) and pore volume (4.7 cm 3 g -1 ). TG/DTA-MS measurement revealed that during storage in ambient conditions surface functional groups formed, which were released upon annealing.