A good number of people take Spirulina as a dietary supplement, but researchers at the Swiss Federal Laboratories for Material Science have found a way to coat the blue-green algae in semiconductor compounds, put the tiny spirals to work removing contaminants from water, and then make biofuels from their remains.
The algae spirals are coated in a nickel, zinc oxide and zinc sulfide combination that was first developed on tiny structures resembling ferns, and were found to be good at absorbing light energy. But moving the process to the spiral shape of the algae avoided a shading problem caused by branches of microferns, resulting in increased light absorption.
The researchers coated four micrometer spirals of preserved Spirulina with a thin layer of nickel, and then layered on zinc oxide and zinc sulfide nanoparticles. The magnetic properties of the nickel proved a good way to recover the coated little spirals, while the zinc coating displayed "impressive photocatalytic activity."
The process was developed to help produce clean water using the purification properties of plants, with a chemical reaction oxidizing and neutralizing pollutants in water when exposed to light. And the combination of zinc oxide and zinc sulfide nanoparticles allowed the team to tap into both the visible and ultraviolet parts of the solar spectrum for improved efficiency.
When the coated spirals have completed their water decontamination task, the zinc and nickel compounds can be recovered and used again. Then bioethanol and biodiesel can be produced from what's left. The remains of the preserved Spirulina can also be processed into pellets and burned to produce energy, and the ash used as fertilizer to cultivate new populations.
The Empa team says that the algae is relatively cheap and easy to produce, needing only water, sunlight and fertilizer to rapidly reproduce. What's more, the unicellular organisms consume carbon dioxide and then throw out oxygen as a waste product – with the process being further improved by adding more CO2 to the algae culture.
At the moment, the process has been successfully demonstrated in a lab setting only, but the researchers say that they are confident that larger scale applications should be possible.
Source: Empa