Chemists develop highly efficient and eco-friendly mini-reactor

Sunflow reactor dramatically accelerates photo-chemical reactions using sunlight as its sole energy source

9 May 2017

Researchers at Johannes Gutenberg University Mainz (JGU) have developed a simple miniature reactor consisting of a thin plastic tube encased in wire mesh in which chemical reactions occur using sunlight as the only energy source at a much faster rate than in standard reactor designs. Not only are reaction times shorter; the set-up is significantly more environmentally-friendly and sustainable. The research team led by Professor Till Opatz at the JGU Institute of Organic Chemistry used a 25-meter long tube, which was wound several times and had an interior diameter of just one millimeter. In this microcapillary flow reactor, sunlight was enough to initiate photochemical reactions of the kind that occur during photosynthesis, for example. "We undertook a total of 13 reactions and saw a drastic increase in the reaction rates," explained Opatz. The sunflow reactor is thus much more efficient than other devices with standard reaction chambers that use low-energy bulbs or LEDs as sources of power.

The growing field of "green chemistry" strives for reactions that combine high yields, renewable starting materials, and energy-efficient techniques that do not require the use of heavy metals or other toxic substances. In the case of photochemical reactions, light radiation supplies the energy that drives specific chemical reactions. However, there are various technological disadvantages associated with large photoreactors. They require relatively long exposure times, which can be problematic if sunlight is the only energy source because they can only be operated in daylight and when the weather is fine.

The sunflow reactor developed by the Mainz team, on the other hand, uses a thin tube that has an extremely large surface area to be exposed to sunlight. The result is that the corresponding reactions are significantly accelerated. The JGU-based chemists were thus able to generate the same yield for certain processes while shortening the reaction time from 16 hours to three minutes. They experimented with the use of different light wavelengths, also with regard to reactions that require UV radiation. "The proportion of UV in sunlight is relatively low, so we were extremely happy about the surprisingly fast conversion rates we achieved," added Opatz. The actual light spectrum employed is generally unimportant as the photons needed for the continuation of the reaction can be filtered out of the sunlight.

"The sunflow reactor we used is easy to build and readily affordable for every research group interested in eco-friendly flow photochemistry," concluded the researchers in their publication. This is the first time that an efficient and eco-friendly set-up that could be used in photoredox and H-atom transfer chemistry has been developed. Professor Till Opatz's team will use the new technique for their own research in the field of photochemistry.