EVER picked a leaf off the ground and looked at its beauty and complexity? Reality is that it is a remarkable harvester of solar energy, the ultimate goal to sustain the plant that it fell from. In the leaf, nature has achieved a great feat of technology. It has succeeded in doing what scientists, with all their sophisticated tools, have been trying to do for decades – using light to drive the splitting of water into its component parts to make a fuel.
The latest step is to try to invent an “artificial leaf” that mimics the real leaf’s chemical magic with photosynthesis – but converts sunlight and water into a liquid fuel such as methanol for cars and trucks. This astonishing revelation was made last year at the first Annual Chemical Sciences and Society Symposium in Germany.
The process involves conversion of water and CO into sugars, as well as oxygen and hydrogen. Scientists have succeeded in mimicking this fuel-making process, termed artificial photosynthesis, but now must find the means of doing so in ways that can be used commercially.
Since the symposium, it has emerged that scientists in China have claimed a significant step forward in the artificial-leaf quest. They used several types of leaves as a template. First, they treated the leaves with dilute hydrochloric acid, allowing them to replace magnesium atoms – which form a crucial part of plants’ photosynthetic machinery – with titanium. Then they dried the leaves and heated them to 500 degrees Centigrade to burn away most of the remaining plant material. This left a crystallised titanium-dioxide framework, plus many of the leaves’ natural structures.
The leaf retained features such as the lens-like cells at its surface, which catch light coming from any angle, and veins that help guide light deeper into the leaf.
A key result is that the “artificial” leaves absorbed more than twice as much light and gave off more than three times as much hydrogen.