Scientists have made a fundamental breakthrough in
their attempts to replicate photosynthesis - the ability of plants to
harvest the power of sunlight - in the hope of making unlimited amounts
of "green" energy from water and sunlight alone.
researchers have assembled genetically modified viruses into wire-like
structures that are able to use the energy of the sun to split water
molecules into their constitute parts of oxygen and hydrogen, which can
then be used as a source of chemical energy.
the process can be scaled up and made more efficient, it promises to
produce unlimited quantities of hydrogen fuel, a clean source of energy
that can be used to generate electricity as well as acting as a portable, carbon-free fuel for cars and other vehicles.
Replicating photosynthesis - in which plants
convert sunlight into a store of chemical energy - has been a dream of
the alternative energy business for decades. The drive was given an
extra boost yesterday with warnings by the US military that there could
be serious global oil shortages by 2015.
water molecules into oxygen and hydrogen is seen as a critical first
step in this process of artificial photosynthesis. Although it is
possible to split the molecules using solar electricity, the process is
not very efficient. In the latest study, scientists were able to split
water directly with sunlight, without using solar panels.
Plants convert sunlight into chemical
energy using the green chlorophyll pigment found in leaves, which traps
packets of light and uses the energy to transport electrons from one
molecular complex to another within the plant's cells. The end result
is the conversion of carbon dioxide and water into glucose, which can
be stored as starch or as other forms of plant carbohydrates.
researchers have tried to emulate this natural photosynthetic process
by using the appropriate parts of plants but these structures tend to
be unstable. Instead, Angela Belcher at the Massachusetts Institute of
Technology borrowed the method rather than using the components of
The scientists genetically engineered a harmless virus called M13, which normally infects bacteria,
so that it would bind to a catalyst called iridium oxide and a
biological pigment, zinc porphyrins. The viruses naturally arranged
themselves into wire-like structures and the catalyst and pigments
effectively harvested sunlight to split the oxygen from the water
Professor Belcher said that the role
of the pigment was to act like an antenna to capture the light and then
transfer the energy down the length of the virus. She said: "The virus
is a very efficient harvester of light, with these porphyrins attached.
We use the components people have used before but we use biology to
organise them for us, so you get better efficiency."
far, the team has only been able to split off oxygen, which is the most
challenging part of the water-splitting process. The hydrogen splits
into its component parts, protons and electrons, and the next stage is
to complete the task of bringing these together in order to collect gas
separately, Professor Belcher said.
published in the journal Nature Nanotechnology, is only the first stage
of a much longer process of development. In addition to refining the
hydrogen-splitting part of the reaction, the scientists still have a
long way to go to increase the efficiency at which sunlight is
converted into chemical energy. Nevertheless, Professor Belcher
predicted that it should be possible to develop the idea into a
prototype commercial product that can carry out the entire
water-splitting process in a durable, self-sustaining way within two
Professor Thomas Mallouk of Pennsylvania
State University, said the research was "an extremely clever piece of
work" that addressed one of the most difficult problems in artificial
photosynthesis by organising molecular components in a manner that
could control the critical transfer of electrons, just like real
He said: "There is a daunting
combination of problems to be solved before this or any other
artificial photosynthetic system could be useful for energy
conversion." For a start, it needs to be at least 10 times more
efficient than natural photosynthesis, to use less expensive material
and to be able to repeat chemical reactions over and over, billions of
Professor Mallouk said: "This is
unlikely to happen in the near future. Nevertheless, the design idea
illustrated in this [study] could ultimately help with an important
piece of the puzzle."
Solar power: Photosynthesis
Photosynthesis is probably the most critical chemical process on earth.
It mostly takes place in tiny structures called chloroplasts found
inside the cells of a plant's leaves.
* The energy that drives the photosynthetic process comes from sunlight and the end product is a store of carbohydrate energy.
A green pigment called chlorophyl traps the sunlight and begins the
process of photosynthesis. It is green because it absorbs light at the
blue ends of the visible light spectrum.
* Photosynthesis is affected by temperature, light intensity, light wavelength and carbon dioxide concentrations.