UNIVERSIDADE FEDERAL DE UBERLÂNDIA Instituto de Química

Programa de Pós Graduação em Química – MESTRADO E-mail: cpgquimica@ufu.br - Fone: 3239-4385

EXAME DE SUFICIÊNCIA EM LÍNGUA INGLESA

1º SEMESTRE DE 2011 – 20/05/2011

PGQ .

CONCEITO: � SUFICIENTE: � INSUFICIENTE

Prof. Antonio Otavio de Toledo Patrocinio

Traduza os textos abaixo para a Língua Portuguesa:

Solar Fuels via Artificial Photosynthesis

Global energy consumption is projected to increase, even in the face of substantial declines

in energy intensity, at least 2-fold by midcentury relative to the present because of population and

economic growth. This demand could be met, in principle, from fossil energy resources, particularly

coal. However, the cumulative nature of CO2 emissions in the atmosphere demands that holding

atmospheric CO2 levels to even twice their preanthropogenic values by midcentury will require

invention, development, and deployment of schemes for carbon-neutral energy production on a

scale commensurate with, or larger than, the entire present-day energy supply from all sources

combined. Among renewable energy resources, solar energy is by far the largest exploitable

resource, providing more energy in 1 hour to the earth than all of the energy consumed by humans

in an entire year. In view of the intermittency of insolation, if solar energy is to be a major primary

energy source, it must be stored and dispatched on demand to the end user. An especially

attractive approach is to store solar-converted energy in the form of chemical bonds, i.e., in a

photosynthetic process at a year-round average efficiency significantly higher than current plants

or algae, to reduce land-area requirements. Scientific challenges involved with this process include

schemes to capture and convert solar energy and then store the energy in the form of chemical

bonds, producing oxygen from water and a reduced fuel such as hydrogen, methane, methanol, or

other hydrocarbon species.

Artificial photosynthesis research applies the fundamental scientific principles of the natural

process to the design of solar energy conversion systems. These devices use different materials,

and researchers tune them to produce energy efficiently and in forms useful to humans. Fuel

production via natural or artificial photosynthesis requires three main components. First,

antenna/reaction center complexes absorb sunlight and convert the excitation energy to

electrochemical energy (redox equivalents). Then, a water oxidation complex uses this redox

potential to catalyze conversion of water to hydrogen ions, electrons stored as reducing

UNIVERSIDADE FEDERAL DE UBERLÂNDIA Instituto de Química

Programa de Pós Graduação em Química – MESTRADO E-mail: cpgquimica@ufu.br - Fone: 3239-4385

equivalents, and oxygen. A second catalytic system uses the reducing equivalents to make fuels

such as carbohydrates, lipids, or hydrogen gas.

A variety of research groups have prepared artificial reaction center molecules. These

systems contain a chromophore, such as a porphyrin, covalently linked to one or more electron

acceptors, such as fullerenes or quinones, and secondary electron donors. Following the excitation

of the chromophore, photoinduced electron transfer generates a primary charge-separated state.

Electron transfer chains spatially separate the redox equivalents and reduce electronic coupling,

slowing recombination of the charge-separated state to the point that catalysts can use the stored

energy for fuel production. Antenna systems, employing a variety of chromophores that absorb

light throughout the visible spectrum, have been coupled to artificial reaction centers and have

incorporated control and photoprotective processes borrowed from photosynthesis. Although

attempts at artificial photosynthesis fall short of the efficiencies necessary for practical application,

they illustrate that solar fuel production inspired by natural photosynthesis is achievable in the

laboratory. For example, artificial reaction centers, where electrons are injected from a dye

molecule into the conduction band of nanoparticulate titanium dioxide on a transparent electrode,

coupled to catalysts, such as platinum or hydrogenase enzymes, can produce hydrogen gas.

Oxidizing equivalents from such reaction centers can be coupled to iridium oxide nanoparticles,

which can oxidize water. More research will be needed to identify the most promising artificial

photosynthetic systems and realize their potential.

Chemistry will assume a special role in this endeavor, because new materials must be

created for solar capture and conversion, and because new catalysts are needed for the desired

chemical bond conversions. The progress of scientists in chemistry, biology, engineering,

materials science, and physics in addressing the basic science challenges involved with realizing

this artificial photosynthesis will be critical to enable humans to use the sun sustainably as their

primary energy source. Adapted from Gust, D.; Moore, T. A.; Moore, A. L., Solar Fuels via Artificial Photosynthesis. Acc. Chem. Res. 2009, 42 (12), 1890-1898. Lewis, N.S.; Nocera, D.G. Powering the Planet: Chemical challenges in solar energy utilization, PNAS, 2006, 103 (43) 15729-15735.