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The spillover mechanism of molecular hydrogen on carbon nanotubes in the presence of catalytically active platinum clusters was critically and systematically investigated by using density-functional theory. Our simulation model includes a Pt4 cluster for the catalyst nanoparticle and curved and planar circumcoronene for two exemplary single-walled carbon nanotubes (CNT), the (10,10) CNT and one of large diameter, respectively. Our results show that the H2 molecule dissociates spontaneously on the Pt4 cluster. However, the dissociated H atoms have to overcome a barrier of more than 2 eV to migrate from the catalyst to the CNT, even if the Pt4 cluster is at full saturation with six adsorbed and dissociated hydrogen molecules. Previous investigations have shown that the mobility of hydrogen atoms on the CNT surface is hindered by a barrier. We find that instead the Pt4 catalyst may move along the outer surface of the CNT with activation energy of only 0.16 eV, and that this effect offers the possibility of full hydrogenation of the CNT. Thus, although we have not found a low-energy pathway to spillover onto the CNT, we suggest, based on our calculations and calculated data reported in the literature, that in the hydrogen-spillover process the observed saturation of the CNT at hydrogen background pressure occurs through mobile Pt nanoclusters, which move on the substrate more easily than the substrate-chemisorbed hydrogens, and deposit or reattach hydrogens in the process. Initial hydrogenation of the carbon substrate, however, is thermodynamically unfavoured, suggesting that defects should play a significant role.

Lithium orthosilicate (Li(4)SiO(4)) was synthesized by solid-state reaction and then its CO(2) chemisorption capacity was evaluated as a function of the CO(2) flow rate and particle size. Initially, a Li(4)SiO(4) sample, with a total surface area of 0.4 m(2)/g, was used to analyze the CO(2) chemisorption, varying the CO(2) flow between 30 and 200 mL/min. Results showed that CO(2) flows modify the kinetic regime from which CO(2) capture is controlled. In the first moments and at low CO(2) flows, the CO(2) capture is controlled by the CO(2) diffusion through the gas-film system, whereas at high CO(2) flows it is controlled by the CO(2) chemisorption reaction rate. Later, at larger times, once the carbonate-oxide external shell has been produced the whole process depends on the CO(2) chemisorption kinetically controlled by the lithium diffusion process, independently of the CO(2) flow. Additionally, thermokinetic analyses suggest that temperature induces a CO(2) particle surface saturation, due to an increment of CO(2) diffusion through the gas-film interface. To elucidate this hypothesis, the Li(4)SiO(4) sample was pulverized to increase the surface area (1.5 m(2)/g). Results showed that increasing the surface particle area, the saturation was not reached. Finally, the enthalpy activation (DeltaH(double dagger)) values were estimated for the two CO(2) chemisorption processes, the CO(2) direct chemisorption produced at the Li(4)SiO(4) surface, and the CO(2) chemisorption kinetically controlled by the lithium diffusion, once the carbonate-oxide shell has been produced.

An efficient sequential, biological and photocatalytic treatment to reduce the pollutant levels in wastewater due to the bleaching process during paper production is reported. For a biological pre-treatment, 800 ml of non-sterilized effluent was inoculated with Trametes versicolor immobilized in polyurethane foam, with 25 g l(-1) glucose, 6.75 mM CuSO(4), and 0.22 mM MnSO(4) added, and cultured at 25 degrees C with an air flow of 800 ml min(-1) for 8d. The fungus did not inhibit growth of the heterotropic populations of the effluent. After 4d of culture, the chemical oxygen demand (COD) reduction and colour removal (CR) were 82% and 80%, respectively, with laccase (LAC) and manganese peroxidase (MnP) activities of 345 U l(-1) and 78 U l(-1), respectively. The COD reduction and CR correlated positively (p<0.0001) with LAC and MnP activities. Chlorophenol removal was 99% of pentachlorophenol, 99% of 2,3,4,6-tetrachlorophenol (2,3,4,6-TCP), 98% of 3,4-dichlorophenol (3,4-DCP) and 77% of 4-chlorophenol (4-CP), while 2,4,5-trichlorophenol (2,4,5-TCP) increased to 0.2 mg l(-1). The pre-treated effluent was then exposed to a photocatalytic treatment. The treatment with photolysis resulted in 9% CR and 46% COD reduction, 42% CR and 60% COD reduction by photocatalysis, and 62% CR and 85% COD reduction by heterogeneous photocatalysis with the system TiO(2)/Ru(x)Se(y) (Fig. 4). With this treatment the bacterial and fungal populations also decreased by 5 logarithmic units with respect to the biological treatment alone (Fig. 5). The total sequential treatment resulted in a 92% CR (from 5800 UC), 97% COD reduction (from 59 g l(-1)) and 99% chlorophenol removal at 96 h and 20 min.