In this paper we describe how the conductivity of a mesoporous TiO2 membrane is strongly affected by the chemistry of the pore walls. We have studied the effect of site density, state of surface protonation, and surface modification in samples with a fixed pore structure. Pore structure was kept fixed by firing all samples at the same temperature. Changing the surface site density (number of water molecules per square nanometer) from 5.5 to 5.7 leads to an increase in conductivity from 8.00 × 10-3 to 1.00 × 10-2 Ω-1 cm-1 at 25 °C and 81% relative humidity (RH). The effect of the state of protonation was studied by pretreating wafers at pH 1.5 and equilibrating them with solutions at pH 2.5 and 4.0. This variable (protonation state of the material) was found to have an even stronger effect on conductivity. Surface modification was achieved by adsorbing phosphate anions from solutions with different pH. It was observed that even a very small degree of phosphate loading (0.71 ions/nm2) leads to an increase in conductivity from 8.27 × 10-3 to 9.66 × 10-3 Ω-1 cm-1 at pH 2.5. The conductivity of our materials, especially those treated at pH 1.5, is very close to that of Nafion, a polymeric material used as a proton conducting membrane in fuel cell systems. The lower cost and higher hydrophilicity of our materials make them potential substitutes for costlier hydrophobic polymeric membranes in fuel cells.

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Recebido em 24/1/09; aceito em 30/3/09; publicado na web em 2/4/09 ENERGY, ENVIRONMENT AND ECONOMY: BRAZIL IN THE WORLD CONTEXT. The cycle of fossil fuels as an energy source for mankind is approaching its end. Finite resources, coupled with greenhouse gas, have led to an increased effort in the search for alternative renewable energy sources. Brazil has a leading position, due to a 46% participation of renewable sources in its primary energy supply, compared to the global average of 12%. The expansion of the renewable sources in Brazil depends on medium and long term planning, and a large volume of investments. The present financial crisis will have major effects in the energy market. Despite a negative initial impact, it is expected that the rearrangement of the financial system will ultimately lead to an expansion in the use of renewable energy sources. Brazil is a tropical country, with the largest biodiversity in our planet and excellent conditions to expand the use of all forms of renewable sources. Keywords: energy; environment; renewable resources. introduÇÃoO panorama mundial está mudando rapidamente, por motivos ligados a três das grandes preocupações da humanidade nesse início de século: meio ambiente, energia e economia global. Embora à primeira vista possam parecer distintas, estas três áreas estão, na realidade, completamente interligadas. As duas primeiras estão já há mais tempo na percepção do cidadão comum, devido ao efeito estufa e ao aquecimento global associado ao uso de combustíveis fósseis. Quanto à economia, só o tempo dirá quais os efeitos permanentes que esta crise no sistema financeiro internacional terá sobre o setor energético e, mais difícil de se prever, sobre o meio ambiente. A única coisa certeza é de que os três setores serão permanentemente afetados.O sistema financeiro não pode ser ignorado. Para se ter uma idéia, o presidente George Bush anunciou em 2006, com grande pompa, um aporte de 1 bilhão de dólares para pesquisas em fontes alternativas de energia, com ênfase no hidrogênio. Estima-se que a crise do sistema financeiro vá consumir algo em torno de 3 trilhões de dólares. A guerra no Iraque já custou aos cofres estadunidenses um valor superior a 500 bilhões de dólares.Não importa qual a saída adotada, ela necessariamente terá que passar por uma mudança radical na matriz energética mundial, com forte aumento da participação das fontes renováveis.Neste contexto, o Brasil se destaca dos demais países por um motivo bem simples: a matriz brasileira já é cerca de 46% renovável, comparada à média mundial de 12%. 1 O Brasil tem, portanto, uma oportunidade ímpar de se firmar como um dos líderes mundiais no setor de energia. Impulsionado por seu gigantesco potencial hídrico e contando com um forte programa de combustíveis alternativos capitaneado pelo etanol, o país sai na frente dos demais. Por outro lado, não podemos desprezar as novas reservas de petróleo recentemente descobertas no litoral brasileiro. Mas, para se manter na frente, serão necessários recursos, muitos recursos: manu...

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Layered double hydroxides (LDHs) containing cadmium as the divalent metal and aluminium as the trivalent metal have been prepared by coprecipitation from a mixed metal nitrate solution, and were obtained with nitrate and carbonate as the counter anions, and as single crystalline phases. XRD patterns show that these LDHs are isostructural with synthetic hydrotalcite, with interlayer spacings of 8.24 and 7.54 Å for Cd/Al/NO 3 and Cd/Al/CO 3 LDHs, respectively. These compounds were intercalated with phenylphosphonic acid (PPA) and 2-carboxyethylphosphonic acid (CEPA). Intercalation is confirmed by XRD, where increased interlayer spacings were observed for the intercalation compounds. Interlayer distances of 14.59 Å were observed for the PPA intercalation compounds, independent of the original counter anion. CEPA intercalated LDHs present interlayer spacings of 11.74 Å for Cd/Al/CEPA obtained from Cd/Al/NO 3 LDH and a double interlayer distance of 11.35 and 12.21 Å for Cd/Al/CEPA obtained from Cd/Al/CO 3 LDH. IR and NMR measurements suggest that this double interlayer spacing is due to the interaction of CEPA to the layers through both of its extremities, i.e. a phosphonate and a carboxylate interaction.

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